2334: update rust january 7 2021 r=bradjc a=hudson-ayers
### Pull Request Overview
This pull request updates the rust nightly version to 2021-01-07. This was motivated by the stabilization of `min_const_generics` ( rust-lang/rust#79135 ) -- by using this nightly, we will be able to use const generics in Tock without adding an unstable feature.
### Testing Strategy
compiling
### TODO or Help Wanted
N/A
### Documentation Updated
- [x] Updated the relevant files in `/docs`.
### Formatting
- [x] Ran `make prepush`.
Co-authored-by: Hudson Ayers <hayers@stanford.edu>

Remove `#![feature(const_generics)]` and `#![allow(incomplete_features)]`
`#![feature(min_const_generics)]` has been [stabilized](rust-lang/rust#79135), so I removed `#![feature(const_generics)]` and `#![allow(incomplete_features)]` (I assume Miri is not built by the beta bootstrap compiler so it's fine to just remove them).
The test [`tests/run-pass/specialization.rs` also has a `#![allow(incomplete_features)]` for `#![feature(specialization)]`](https://github.com/rust-lang/miri/blob/9949d9e4/tests/run-pass/specialization.rs#L1-L2). I think that can be removed and `#![feature(specialization)]` can be replaced with `#![feature(min_specialization)]`, but I'm not sure whether I should do that because it's a test. Feel free to ask me to remove it if it's fine to do so.

205: Generalizing gradients and add constant gradients r=Ogeon a=NicolasKlenert
This pull request contains two commits:
### 1. Generalization of  `Gradient`
This allows creation of gradients from arrays. The inner collection type only has to be `ArrayLike`. For backward compatibility the default is still vector. This allows constant gradients and should also allow gradients to be supported for the next `#[no-std]` build. Other options to enable `#[no-std]` for gradients were briefly disscused in #156.
### 2. Adding some constant gradients
This commit adds constant gradients. To be precise, it adds all 4 new matplotlib color gradients, which are perfectly perceptually-uniform, both in regular form and also when converted to black-and-white and therefore one of the most useful gradients. These are build the same way the named colors are built. A new feature-flag `named_gradients` is added to toggle said constants. This closes #62.
### Alterantives
- The generalization of gradients can be achieved in a multiple of ways. Using a trait is just one of them and may be the wrong way to go.
   - However I think because this pull request doesn't have any breaking changes and gradients should be supporting arrays in future versions of the crate, it doesn't seem like this update of  `Gradient` will cause more breaking API changes in the future than otherwise. Also constant gradients may be the only interaction with gradients a user needs, such that introducing them could reduce the number of users which actually relies on the generation of `Gradient` itself.
- At the moment the 4 constant gradients are using linear interpolation but in nature these gradients are Spline-Interpolations of exaclty two points (and 2 controlpoints). If `Gradient` will support Spline-Inerpolation in the future and the exact controlpoints of these gradients can be found (I only found the colormaps), the gradients could be implemented more memory efficient.
### Remark
These commits depend on const generics, which is a feature in beta but is planned to be stable on 2021-03-25 onwords (see [#79135](rust-lang/rust#79135)).
Co-authored-by: Nicolas Klenert <klenert.nicolas@gmail.com>
Co-authored-by: NicolasKlenert <Nicolas_Klenert@web.de>
Co-authored-by: NicolasKlenert <klenert.nicolas@gmail.com>

Pkgsrc changes:
 * Remove one SunOS patch, apparently no longer needed.
 * Adapt one patch for Darwin, adjust cargo checksum accordingly.
 * Adjust bootstraps to version 1.50.0.
Version 1.51.0 (2021-03-25)
============================
Language
--------
- [You can now parameterize items such as functions, traits, and
  `struct`s by constant values in addition to by types and
  lifetimes.][79135] Also known as "const generics" E.g. you can
  now write the following. Note:  Only values of primitive integers,
  `bool`, or `char` types are currently permitted.
  ```rust
  struct GenericArray<T, const LENGTH: usize> {
      inner: [T; LENGTH]
  }
  impl<T, const LENGTH: usize> GenericArray<T, LENGTH> {
      const fn last(&self) -> Option<&T> {
          if LENGTH == 0 {
              None
          } else {
              Some(&self.inner[LENGTH - 1])
          }
      }
  }
  ```
Compiler
--------
- [Added the `-Csplit-debuginfo` codegen option for macOS platforms.][79570]
  This option controls whether debug information is split across
  multiple files or packed into a single file. **Note** This option
  is unstable on other platforms.
- [Added tier 3\* support for `aarch64_be-unknown-linux-gnu`,
  `aarch64-unknown-linux-gnu_ilp32`, and
  `aarch64_be-unknown-linux-gnu_ilp32` targets.][81455]
- [Added tier 3 support for `i386-unknown-linux-gnu` and
  `i486-unknown-linux-gnu` targets.][80662]
- [The `target-cpu=native` option will now detect individual features
  of CPUs.][80749]
- [Rust now uses `inline-asm` for stack probes when used with LLVM
  11.0.1+][77885]
\* Refer to Rust's [platform support page][forge-platform-support]
for more information on Rust's tiered platform support.
Libraries
---------
- [`Box::downcast` is now also implemented for any `dyn Any + Send
  + Sync` object.][80945]
- [`str` now implements `AsMut<str>`.][80279]
- [`u64` and `u128` now implement `From<char>`.][79502]
- [`Error` is now implemented for `&T` where `T` implements `Error`.][75180]
- [`Poll::{map_ok, map_err}` are now implemented for `Poll<Option<Result<T,
  E>>>`.][80968]
- [`unsigned_abs` is now implemented for all signed integer types.][80959]
- [`io::Empty` now implements `io::Seek`.][78044]
- [`rc::Weak<T>` and `sync::Weak<T>`'s methods such as `as_ptr`
  are now implemented for `T: ?Sized` types.][80764]
Stabilized APIs
---------------
- [`Arc::decrement_strong_count`]
- [`Arc::increment_strong_count`]
- [`Once::call_once_force`]
- [`Peekable::next_if_eq`]
- [`Peekable::next_if`]
- [`Seek::stream_position`]
- [`array::IntoIter`]
- [`panic::panic_any`]
- [`ptr::addr_of!`]
- [`ptr::addr_of_mut!`]
- [`slice::fill_with`]
- [`slice::split_inclusive_mut`]
- [`slice::split_inclusive`]
- [`slice::strip_prefix`]
- [`slice::strip_suffix`]
- [`str::split_inclusive`]
- [`sync::OnceState`]
- [`task::Wake`]
Cargo
-----
- [Added the `split-debuginfo` profile option to control the -Csplit-debuginfo
  codegen option.][cargo/9112]
- [Added the `resolver` field to `Cargo.toml` to enable the new
  feature resolver and CLI option behavior.][cargo/8997] Version
  2 of the feature resolver will try to avoid unifying features of
  dependencies where that unification could be unwanted.  Such as
  using the same dependency with a `std` feature in a build scripts
  and proc-macros, while using the `no-std` feature in the final
  binary. See the [Cargo book documentation][feature-resolver@2.0]
  for more information on the feature.
Rustdoc
-------
- [Rustdoc will now include documentation for methods available
  from `Deref` traits.][80653]
- [You can now provide a `--default-theme` flag which sets the
  default theme to use for documentation.][79642]
Various improvements to intra-doc links:
- [You can link to non-path primitives such as `slice`.][80181]
- [You can link to associated items.][74489]
- [You can now include generic parameters when linking to items,
  like `Vec<T>`.][76934]
Misc
----
- [You can now pass `--include-ignored` to tests (e.g. with
  `cargo test -- --include-ignored`) to include testing tests marked
  `#[ignore]`.][80053]
Compatibility Notes
-------------------
- [WASI platforms no longer use the `wasm-bindgen` ABI, and instead
  use the wasm32 ABI.][79998]
- [`rustc` no longer promotes division, modulo and indexing operations
  to `const` that could fail.][80579]
- [The minimum version of glibc for the following platforms has
  been bumped to version 2.31 for the distributed artifacts.][81521]
    - `armv5te-unknown-linux-gnueabi`
    - `sparc64-unknown-linux-gnu`
    - `thumbv7neon-unknown-linux-gnueabihf`
    - `armv7-unknown-linux-gnueabi`
    - `x86_64-unknown-linux-gnux32`
Internal Only
-------------
- [Consistently avoid constructing optimized MIR when not doing codegen][80718]
[79135]: rust-lang/rust#79135
[74489]: rust-lang/rust#74489
[76934]: rust-lang/rust#76934
[79570]: rust-lang/rust#79570
[80181]: rust-lang/rust#80181
[79642]: rust-lang/rust#79642
[80945]: rust-lang/rust#80945
[80279]: rust-lang/rust#80279
[80053]: rust-lang/rust#80053
[79502]: rust-lang/rust#79502
[75180]: rust-lang/rust#75180
[79135]: rust-lang/rust#79135
[81521]: rust-lang/rust#81521
[80968]: rust-lang/rust#80968
[80959]: rust-lang/rust#80959
[80718]: rust-lang/rust#80718
[80653]: rust-lang/rust#80653
[80579]: rust-lang/rust#80579
[79998]: rust-lang/rust#79998
[78044]: rust-lang/rust#78044
[81455]: rust-lang/rust#81455
[80764]: rust-lang/rust#80764
[80749]: rust-lang/rust#80749
[80662]: rust-lang/rust#80662
[77885]: rust-lang/rust#77885
[cargo/8997]: rust-lang/cargo#8997
[cargo/9112]: rust-lang/cargo#9112
[feature-resolver@2.0]: https://doc.rust-lang.org/nightly/cargo/reference/features.html#feature-resolver-version-2
[`Once::call_once_force`]: https://doc.rust-lang.org/stable/std/sync/struct.Once.html#method.call_once_force
[`sync::OnceState`]: https://doc.rust-lang.org/stable/std/sync/struct.OnceState.html
[`panic::panic_any`]: https://doc.rust-lang.org/stable/std/panic/fn.panic_any.html
[`slice::strip_prefix`]: https://doc.rust-lang.org/stable/std/primitive.slice.html#method.strip_prefix
[`slice::strip_suffix`]: https://doc.rust-lang.org/stable/std/primitive.slice.html#method.strip_prefix
[`Arc::increment_strong_count`]: https://doc.rust-lang.org/nightly/std/sync/struct.Arc.html#method.increment_strong_count
[`Arc::decrement_strong_count`]: https://doc.rust-lang.org/nightly/std/sync/struct.Arc.html#method.decrement_strong_count
[`slice::fill_with`]: https://doc.rust-lang.org/nightly/std/primitive.slice.html#method.fill_with
[`ptr::addr_of!`]: https://doc.rust-lang.org/nightly/std/ptr/macro.addr_of.html
[`ptr::addr_of_mut!`]: https://doc.rust-lang.org/nightly/std/ptr/macro.addr_of_mut.html
[`array::IntoIter`]: https://doc.rust-lang.org/nightly/std/array/struct.IntoIter.html
[`slice::split_inclusive`]: https://doc.rust-lang.org/nightly/std/primitive.slice.html#method.split_inclusive
[`slice::split_inclusive_mut`]: https://doc.rust-lang.org/nightly/std/primitive.slice.html#method.split_inclusive_mut
[`str::split_inclusive`]: https://doc.rust-lang.org/nightly/std/primitive.str.html#method.split_inclusive
[`task::Wake`]: https://doc.rust-lang.org/nightly/std/task/trait.Wake.html
[`Seek::stream_position`]: https://doc.rust-lang.org/nightly/std/io/trait.Seek.html#method.stream_position
[`Peekable::next_if`]: https://doc.rust-lang.org/nightly/std/iter/struct.Peekable.html#method.next_if
[`Peekable::next_if_eq`]: https://doc.rust-lang.org/nightly/std/iter/struct.Peekable.html#method.next_if_eq

Pkgsrc changes:
 * Add support for the big-endian arm64 NetBSD target (aarch64_be).
 * On NetBSD/i386, use the i586 (pentium) bootstrap kit variant in
   preference to i686.
 * Adjust patches, re-compute line offsets, re-compute crate checksums.
 * Remove a patch which was either integrated upstream and/or no longer
   applies.
 * Bump bootstraps to 1.50.0.
 * Move conditionals until after bsd.prefs.mk so that they work...
 * Default to "dist" build target if cross-compiling, but allow
   also to override via rust.BUILD_TARGET.
 * Allow overriding MAKE_JOBS_SAFE via rust.MAKE_JOBS_SAFE if you
   want a different trade-off between occasional breakage and performance.
 * Adjust platform.mk according to work already done in wip/rust/
 * Add a patch to optimize the install.sh script used to install binary
   bootstraps to not do so many forks; use case/esac and parameter expansion
   instead of grep, sed and cut.
 * Drop building documentation for the binary bootstrap kits.  This will
   also impact the lang/rust-bin package.  For full documentation, build
   or install lang/rust as a package.
Upstream changes:
Version 1.51.0 (2021-03-25)
============================
Language
--------
- [You can now parameterize items such as functions, traits, and
  `struct`s by constant values in addition to by types and
  lifetimes.][79135] Also known as "const generics" E.g. you can
  now write the following. Note:  Only values of primitive integers,
  `bool`, or `char` types are currently permitted.
  ```rust
  struct GenericArray<T, const LENGTH: usize> {
      inner: [T; LENGTH]
  }
  impl<T, const LENGTH: usize> GenericArray<T, LENGTH> {
      const fn last(&self) -> Option<&T> {
          if LENGTH == 0 {
              None
          } else {
              Some(&self.inner[LENGTH - 1])
          }
      }
  }
  ```
Compiler
--------
- [Added the `-Csplit-debuginfo` codegen option for macOS platforms.][79570]
  This option controls whether debug information is split across
  multiple files or packed into a single file. **Note** This option
  is unstable on other platforms.
- [Added tier 3\* support for `aarch64_be-unknown-linux-gnu`,
  `aarch64-unknown-linux-gnu_ilp32`, and
  `aarch64_be-unknown-linux-gnu_ilp32` targets.][81455]
- [Added tier 3 support for `i386-unknown-linux-gnu` and
  `i486-unknown-linux-gnu` targets.][80662]
- [The `target-cpu=native` option will now detect individual features
  of CPUs.][80749]
\* Refer to Rust's [platform support page][platform-support-doc] for more
information on Rust's tiered platform support.
Libraries
---------
- [`Box::downcast` is now also implemented for any `dyn Any + Send
  + Sync` object.][80945]
- [`str` now implements `AsMut<str>`.][80279]
- [`u64` and `u128` now implement `From<char>`.][79502]
- [`Error` is now implemented for `&T` where `T` implements `Error`.][75180]
- [`Poll::{map_ok, map_err}` are now implemented for
  `Poll<Option<Result<T,E>>>`.][80968]
- [`unsigned_abs` is now implemented for all signed integer types.][80959]
- [`io::Empty` now implements `io::Seek`.][78044]
- [`rc::Weak<T>` and `sync::Weak<T>`'s methods such as `as_ptr`
  are now implemented for `T: ?Sized` types.][80764]
- [`Div` and `Rem` by their `NonZero` variant is now implemented
  for all unsigned integers.][79134]
Stabilized APIs
---------------
- [`Arc::decrement_strong_count`]
- [`Arc::increment_strong_count`]
- [`Once::call_once_force`]
- [`Peekable::next_if_eq`]
- [`Peekable::next_if`]
- [`Seek::stream_position`]
- [`array::IntoIter`]
- [`panic::panic_any`]
- [`ptr::addr_of!`]
- [`ptr::addr_of_mut!`]
- [`slice::fill_with`]
- [`slice::split_inclusive_mut`]
- [`slice::split_inclusive`]
- [`slice::strip_prefix`]
- [`slice::strip_suffix`]
- [`str::split_inclusive`]
- [`sync::OnceState`]
- [`task::Wake`]
- [`VecDeque::range`]
- [`VecDeque::range_mut`]
Cargo
-----
- [Added the `split-debuginfo` profile option to control the -Csplit-debuginfo
  codegen option.][cargo/9112]
- [Added the `resolver` field to `Cargo.toml` to enable the new
  feature resolver and CLI option behavior.][cargo/8997] Version
  2 of the feature resolver will try to avoid unifying features of
  dependencies where that unification could be unwanted.  Such as
  using the same dependency with a `std` feature in a build scripts
  and proc-macros, while using the `no-std` feature in the final
  binary. See the [Cargo book documentation][feature-resolver@2.0]
  for more information on the feature.
Rustdoc
-------
- [Rustdoc will now include documentation for methods available
  from _nested_ `Deref` traits.][80653]
- [You can now provide a `--default-theme` flag which sets the
  default theme to use for documentation.][79642]
Various improvements to intra-doc links:
- [You can link to non-path primitives such as `slice`.][80181]
- [You can link to associated items.][74489]
- [You can now include generic parameters when linking to items,
  like `Vec<T>`.][76934]
Misc
----
- [You can now pass `--include-ignored` to tests (e.g. with
  `cargo test -- --include-ignored`) to include testing tests marked
  `#[ignore]`.][80053]
Compatibility Notes
-------------------
- [WASI platforms no longer use the `wasm-bindgen` ABI, and instead
  use the wasm32 ABI.][79998]
- [`rustc` no longer promotes division, modulo and indexing operations
  to `const` that could fail.][80579]
- [The minimum version of glibc for the following platforms has
  been bumped to version 2.31 for the distributed artifacts.][81521]
    - `armv5te-unknown-linux-gnueabi`
    - `sparc64-unknown-linux-gnu`
    - `thumbv7neon-unknown-linux-gnueabihf`
    - `armv7-unknown-linux-gnueabi`
    - `x86_64-unknown-linux-gnux32`
- [`atomic::spin_loop_hint` has been deprecated.][80966] It's
  recommended to use `hint::spin_loop` instead.
Internal Only
-------------
- [Consistently avoid constructing optimized MIR when not doing codegen][80718]
[79135]: rust-lang/rust#79135
[74489]: rust-lang/rust#74489
[76934]: rust-lang/rust#76934
[79570]: rust-lang/rust#79570
[80181]: rust-lang/rust#80181
[79642]: rust-lang/rust#79642
[80945]: rust-lang/rust#80945
[80279]: rust-lang/rust#80279
[80053]: rust-lang/rust#80053
[79502]: rust-lang/rust#79502
[75180]: rust-lang/rust#75180
[79135]: rust-lang/rust#79135
[81521]: rust-lang/rust#81521
[80968]: rust-lang/rust#80968
[80959]: rust-lang/rust#80959
[80718]: rust-lang/rust#80718
[80653]: rust-lang/rust#80653
[80579]: rust-lang/rust#80579
[79998]: rust-lang/rust#79998
[78044]: rust-lang/rust#78044
[81455]: rust-lang/rust#81455
[80764]: rust-lang/rust#80764
[80749]: rust-lang/rust#80749
[80662]: rust-lang/rust#80662
[79134]: rust-lang/rust#79134
[80966]: rust-lang/rust#80966
[cargo/8997]: rust-lang/cargo#8997
[cargo/9112]: rust-lang/cargo#9112
[feature-resolver@2.0]: https://doc.rust-lang.org/nightly/cargo/reference/features.html#feature-resolver-version-2
[`Once::call_once_force`]: https://doc.rust-lang.org/stable/std/sync/struct.Once.html#method.call_once_force
[`sync::OnceState`]: https://doc.rust-lang.org/stable/std/sync/struct.OnceState.html
[`panic::panic_any`]: https://doc.rust-lang.org/stable/std/panic/fn.panic_any.html
[`slice::strip_prefix`]: https://doc.rust-lang.org/stable/std/primitive.slice.html#method.strip_prefix
[`slice::strip_suffix`]: https://doc.rust-lang.org/stable/std/primitive.slice.html#method.strip_prefix
[`Arc::increment_strong_count`]: https://doc.rust-lang.org/nightly/std/sync/struct.Arc.html#method.increment_strong_count
[`Arc::decrement_strong_count`]: https://doc.rust-lang.org/nightly/std/sync/struct.Arc.html#method.decrement_strong_count
[`slice::fill_with`]: https://doc.rust-lang.org/nightly/std/primitive.slice.html#method.fill_with
[`ptr::addr_of!`]: https://doc.rust-lang.org/nightly/std/ptr/macro.addr_of.html
[`ptr::addr_of_mut!`]: https://doc.rust-lang.org/nightly/std/ptr/macro.addr_of_mut.html
[`array::IntoIter`]: https://doc.rust-lang.org/nightly/std/array/struct.IntoIter.html
[`slice::split_inclusive`]: https://doc.rust-lang.org/nightly/std/primitive.slice.html#method.split_inclusive
[`slice::split_inclusive_mut`]: https://doc.rust-lang.org/nightly/std/primitive.slice.html#method.split_inclusive_mut
[`str::split_inclusive`]: https://doc.rust-lang.org/nightly/std/primitive.str.html#method.split_inclusive
[`task::Wake`]: https://doc.rust-lang.org/nightly/std/task/trait.Wake.html
[`Seek::stream_position`]: https://doc.rust-lang.org/nightly/std/io/trait.Seek.html#method.stream_position
[`Peekable::next_if`]: https://doc.rust-lang.org/nightly/std/iter/struct.Peekable.html#method.next_if
[`Peekable::next_if_eq`]: https://doc.rust-lang.org/nightly/std/iter/struct.Peekable.html#method.next_if_eq
[`VecDeque::range`]: https://doc.rust-lang.org/nightly/std/collections/struct.VecDeque.html#method.range
[`VecDeque::range_mut`]: https://doc.rust-lang.org/nightly/std/collections/struct.VecDeque.html#method.range_mut

This was possible thanks to the [stabilisation of minimal const generics
support](rust-lang/rust#79135) in Rust 1.51.

Pkgsrc changes:
 * Add support for the big-endian arm64 NetBSD target (aarch64_be).
 * On NetBSD/i386, use the i586 (pentium) bootstrap kit variant in
   preference to i686.
 * Adjust patches, re-compute line offsets, re-compute crate checksums.
 * Remove a patch which was either integrated upstream and/or no longer
   applies.
 * Bump bootstraps to 1.50.0.
 * Move conditionals until after bsd.prefs.mk so that they work...
 * Default to "dist" build target if cross-compiling, but allow
   also to override via rust.BUILD_TARGET.
 * Allow overriding MAKE_JOBS_SAFE via rust.MAKE_JOBS_SAFE if you
   want a different trade-off between occasional breakage and performance.
 * Adjust platform.mk according to work already done in wip/rust/
 * Add a patch to optimize the install.sh script used to install binary
   bootstraps to not do so many forks; use case/esac and parameter expansion
   instead of grep, sed and cut.
 * Drop building documentation for the binary bootstrap kits.  This will
   also impact the lang/rust-bin package.  For full documentation, build
   or install lang/rust as a package.
Upstream changes:
Version 1.51.0 (2021-03-25)
============================
Language
--------
- [You can now parameterize items such as functions, traits, and
  `struct`s by constant values in addition to by types and
  lifetimes.][79135] Also known as "const generics" E.g. you can
  now write the following. Note:  Only values of primitive integers,
  `bool`, or `char` types are currently permitted.
  ```rust
  struct GenericArray<T, const LENGTH: usize> {
      inner: [T; LENGTH]
  }
  impl<T, const LENGTH: usize> GenericArray<T, LENGTH> {
      const fn last(&self) -> Option<&T> {
          if LENGTH == 0 {
              None
          } else {
              Some(&self.inner[LENGTH - 1])
          }
      }
  }
  ```
Compiler
--------
- [Added the `-Csplit-debuginfo` codegen option for macOS platforms.][79570]
  This option controls whether debug information is split across
  multiple files or packed into a single file. **Note** This option
  is unstable on other platforms.
- [Added tier 3\* support for `aarch64_be-unknown-linux-gnu`,
  `aarch64-unknown-linux-gnu_ilp32`, and
  `aarch64_be-unknown-linux-gnu_ilp32` targets.][81455]
- [Added tier 3 support for `i386-unknown-linux-gnu` and
  `i486-unknown-linux-gnu` targets.][80662]
- [The `target-cpu=native` option will now detect individual features
  of CPUs.][80749]
\* Refer to Rust's [platform support page][platform-support-doc] for more
information on Rust's tiered platform support.
Libraries
---------
- [`Box::downcast` is now also implemented for any `dyn Any + Send
  + Sync` object.][80945]
- [`str` now implements `AsMut<str>`.][80279]
- [`u64` and `u128` now implement `From<char>`.][79502]
- [`Error` is now implemented for `&T` where `T` implements `Error`.][75180]
- [`Poll::{map_ok, map_err}` are now implemented for
  `Poll<Option<Result<T,E>>>`.][80968]
- [`unsigned_abs` is now implemented for all signed integer types.][80959]
- [`io::Empty` now implements `io::Seek`.][78044]
- [`rc::Weak<T>` and `sync::Weak<T>`'s methods such as `as_ptr`
  are now implemented for `T: ?Sized` types.][80764]
- [`Div` and `Rem` by their `NonZero` variant is now implemented
  for all unsigned integers.][79134]
Stabilized APIs
---------------
- [`Arc::decrement_strong_count`]
- [`Arc::increment_strong_count`]
- [`Once::call_once_force`]
- [`Peekable::next_if_eq`]
- [`Peekable::next_if`]
- [`Seek::stream_position`]
- [`array::IntoIter`]
- [`panic::panic_any`]
- [`ptr::addr_of!`]
- [`ptr::addr_of_mut!`]
- [`slice::fill_with`]
- [`slice::split_inclusive_mut`]
- [`slice::split_inclusive`]
- [`slice::strip_prefix`]
- [`slice::strip_suffix`]
- [`str::split_inclusive`]
- [`sync::OnceState`]
- [`task::Wake`]
- [`VecDeque::range`]
- [`VecDeque::range_mut`]
Cargo
-----
- [Added the `split-debuginfo` profile option to control the -Csplit-debuginfo
  codegen option.][cargo/9112]
- [Added the `resolver` field to `Cargo.toml` to enable the new
  feature resolver and CLI option behavior.][cargo/8997] Version
  2 of the feature resolver will try to avoid unifying features of
  dependencies where that unification could be unwanted.  Such as
  using the same dependency with a `std` feature in a build scripts
  and proc-macros, while using the `no-std` feature in the final
  binary. See the [Cargo book documentation][feature-resolver@2.0]
  for more information on the feature.
Rustdoc
-------
- [Rustdoc will now include documentation for methods available
  from _nested_ `Deref` traits.][80653]
- [You can now provide a `--default-theme` flag which sets the
  default theme to use for documentation.][79642]
Various improvements to intra-doc links:
- [You can link to non-path primitives such as `slice`.][80181]
- [You can link to associated items.][74489]
- [You can now include generic parameters when linking to items,
  like `Vec<T>`.][76934]
Misc
----
- [You can now pass `--include-ignored` to tests (e.g. with
  `cargo test -- --include-ignored`) to include testing tests marked
  `#[ignore]`.][80053]
Compatibility Notes
-------------------
- [WASI platforms no longer use the `wasm-bindgen` ABI, and instead
  use the wasm32 ABI.][79998]
- [`rustc` no longer promotes division, modulo and indexing operations
  to `const` that could fail.][80579]
- [The minimum version of glibc for the following platforms has
  been bumped to version 2.31 for the distributed artifacts.][81521]
    - `armv5te-unknown-linux-gnueabi`
    - `sparc64-unknown-linux-gnu`
    - `thumbv7neon-unknown-linux-gnueabihf`
    - `armv7-unknown-linux-gnueabi`
    - `x86_64-unknown-linux-gnux32`
- [`atomic::spin_loop_hint` has been deprecated.][80966] It's
  recommended to use `hint::spin_loop` instead.
Internal Only
-------------
- [Consistently avoid constructing optimized MIR when not doing codegen][80718]
[79135]: rust-lang/rust#79135
[74489]: rust-lang/rust#74489
[76934]: rust-lang/rust#76934
[79570]: rust-lang/rust#79570
[80181]: rust-lang/rust#80181
[79642]: rust-lang/rust#79642
[80945]: rust-lang/rust#80945
[80279]: rust-lang/rust#80279
[80053]: rust-lang/rust#80053
[79502]: rust-lang/rust#79502
[75180]: rust-lang/rust#75180
[79135]: rust-lang/rust#79135
[81521]: rust-lang/rust#81521
[80968]: rust-lang/rust#80968
[80959]: rust-lang/rust#80959
[80718]: rust-lang/rust#80718
[80653]: rust-lang/rust#80653
[80579]: rust-lang/rust#80579
[79998]: rust-lang/rust#79998
[78044]: rust-lang/rust#78044
[81455]: rust-lang/rust#81455
[80764]: rust-lang/rust#80764
[80749]: rust-lang/rust#80749
[80662]: rust-lang/rust#80662
[79134]: rust-lang/rust#79134
[80966]: rust-lang/rust#80966
[cargo/8997]: rust-lang/cargo#8997
[cargo/9112]: rust-lang/cargo#9112
[feature-resolver@2.0]: https://doc.rust-lang.org/nightly/cargo/reference/features.html#feature-resolver-version-2
[`Once::call_once_force`]: https://doc.rust-lang.org/stable/std/sync/struct.Once.html#method.call_once_force
[`sync::OnceState`]: https://doc.rust-lang.org/stable/std/sync/struct.OnceState.html
[`panic::panic_any`]: https://doc.rust-lang.org/stable/std/panic/fn.panic_any.html
[`slice::strip_prefix`]: https://doc.rust-lang.org/stable/std/primitive.slice.html#method.strip_prefix
[`slice::strip_suffix`]: https://doc.rust-lang.org/stable/std/primitive.slice.html#method.strip_prefix
[`Arc::increment_strong_count`]: https://doc.rust-lang.org/nightly/std/sync/struct.Arc.html#method.increment_strong_count
[`Arc::decrement_strong_count`]: https://doc.rust-lang.org/nightly/std/sync/struct.Arc.html#method.decrement_strong_count
[`slice::fill_with`]: https://doc.rust-lang.org/nightly/std/primitive.slice.html#method.fill_with
[`ptr::addr_of!`]: https://doc.rust-lang.org/nightly/std/ptr/macro.addr_of.html
[`ptr::addr_of_mut!`]: https://doc.rust-lang.org/nightly/std/ptr/macro.addr_of_mut.html
[`array::IntoIter`]: https://doc.rust-lang.org/nightly/std/array/struct.IntoIter.html
[`slice::split_inclusive`]: https://doc.rust-lang.org/nightly/std/primitive.slice.html#method.split_inclusive
[`slice::split_inclusive_mut`]: https://doc.rust-lang.org/nightly/std/primitive.slice.html#method.split_inclusive_mut
[`str::split_inclusive`]: https://doc.rust-lang.org/nightly/std/primitive.str.html#method.split_inclusive
[`task::Wake`]: https://doc.rust-lang.org/nightly/std/task/trait.Wake.html
[`Seek::stream_position`]: https://doc.rust-lang.org/nightly/std/io/trait.Seek.html#method.stream_position
[`Peekable::next_if`]: https://doc.rust-lang.org/nightly/std/iter/struct.Peekable.html#method.next_if
[`Peekable::next_if_eq`]: https://doc.rust-lang.org/nightly/std/iter/struct.Peekable.html#method.next_if_eq
[`VecDeque::range`]: https://doc.rust-lang.org/nightly/std/collections/struct.VecDeque.html#method.range
[`VecDeque::range_mut`]: https://doc.rust-lang.org/nightly/std/collections/struct.VecDeque.html#method.range_mut

2334: update rust january 7 2021 r=bradjc a=hudson-ayers
### Pull Request Overview
This pull request updates the rust nightly version to 2021-01-07. This was motivated by the stabilization of `min_const_generics` ( rust-lang/rust#79135 ) -- by using this nightly, we will be able to use const generics in Tock without adding an unstable feature.
### Testing Strategy
compiling
### TODO or Help Wanted
N/A
### Documentation Updated
- [x] Updated the relevant files in `/docs`.
### Formatting
- [x] Ran `make prepush`.
Co-authored-by: Hudson Ayers <hayers@stanford.edu>

Pkgsrc changes:
 * Add support for the big-endian arm64 NetBSD target (aarch64_be).
 * On NetBSD/i386, use the i586 (pentium) bootstrap kit variant in
   preference to i686.
 * Adjust patches, re-compute line offsets, re-compute crate checksums.
 * Remove a patch which was either integrated upstream and/or no longer
   applies.
 * Bump bootstraps to 1.50.0.
 * Move conditionals until after bsd.prefs.mk so that they work...
 * Default to "dist" build target if cross-compiling, but allow
   also to override via rust.BUILD_TARGET.
 * Allow overriding MAKE_JOBS_SAFE via rust.MAKE_JOBS_SAFE if you
   want a different trade-off between occasional breakage and performance.
 * Adjust platform.mk according to work already done in wip/rust/
 * Add a patch to optimize the install.sh script used to install binary
   bootstraps to not do so many forks; use case/esac and parameter expansion
   instead of grep, sed and cut.
 * Drop building documentation for the binary bootstrap kits.  This will
   also impact the lang/rust-bin package.  For full documentation, build
   or install lang/rust as a package.
Upstream changes:
Version 1.51.0 (2021-03-25)
============================
Language
--------
- [You can now parameterize items such as functions, traits, and
  `struct`s by constant values in addition to by types and
  lifetimes.][79135] Also known as "const generics" E.g. you can
  now write the following. Note:  Only values of primitive integers,
  `bool`, or `char` types are currently permitted.
  ```rust
  struct GenericArray<T, const LENGTH: usize> {
      inner: [T; LENGTH]
  }
  impl<T, const LENGTH: usize> GenericArray<T, LENGTH> {
      const fn last(&self) -> Option<&T> {
          if LENGTH == 0 {
              None
          } else {
              Some(&self.inner[LENGTH - 1])
          }
      }
  }
  ```
Compiler
--------
- [Added the `-Csplit-debuginfo` codegen option for macOS platforms.][79570]
  This option controls whether debug information is split across
  multiple files or packed into a single file. **Note** This option
  is unstable on other platforms.
- [Added tier 3\* support for `aarch64_be-unknown-linux-gnu`,
  `aarch64-unknown-linux-gnu_ilp32`, and
  `aarch64_be-unknown-linux-gnu_ilp32` targets.][81455]
- [Added tier 3 support for `i386-unknown-linux-gnu` and
  `i486-unknown-linux-gnu` targets.][80662]
- [The `target-cpu=native` option will now detect individual features
  of CPUs.][80749]
\* Refer to Rust's [platform support page][platform-support-doc] for more
information on Rust's tiered platform support.
Libraries
---------
- [`Box::downcast` is now also implemented for any `dyn Any + Send
  + Sync` object.][80945]
- [`str` now implements `AsMut<str>`.][80279]
- [`u64` and `u128` now implement `From<char>`.][79502]
- [`Error` is now implemented for `&T` where `T` implements `Error`.][75180]
- [`Poll::{map_ok, map_err}` are now implemented for
  `Poll<Option<Result<T,E>>>`.][80968]
- [`unsigned_abs` is now implemented for all signed integer types.][80959]
- [`io::Empty` now implements `io::Seek`.][78044]
- [`rc::Weak<T>` and `sync::Weak<T>`'s methods such as `as_ptr`
  are now implemented for `T: ?Sized` types.][80764]
- [`Div` and `Rem` by their `NonZero` variant is now implemented
  for all unsigned integers.][79134]
Stabilized APIs
---------------
- [`Arc::decrement_strong_count`]
- [`Arc::increment_strong_count`]
- [`Once::call_once_force`]
- [`Peekable::next_if_eq`]
- [`Peekable::next_if`]
- [`Seek::stream_position`]
- [`array::IntoIter`]
- [`panic::panic_any`]
- [`ptr::addr_of!`]
- [`ptr::addr_of_mut!`]
- [`slice::fill_with`]
- [`slice::split_inclusive_mut`]
- [`slice::split_inclusive`]
- [`slice::strip_prefix`]
- [`slice::strip_suffix`]
- [`str::split_inclusive`]
- [`sync::OnceState`]
- [`task::Wake`]
- [`VecDeque::range`]
- [`VecDeque::range_mut`]
Cargo
-----
- [Added the `split-debuginfo` profile option to control the -Csplit-debuginfo
  codegen option.][cargo/9112]
- [Added the `resolver` field to `Cargo.toml` to enable the new
  feature resolver and CLI option behavior.][cargo/8997] Version
  2 of the feature resolver will try to avoid unifying features of
  dependencies where that unification could be unwanted.  Such as
  using the same dependency with a `std` feature in a build scripts
  and proc-macros, while using the `no-std` feature in the final
  binary. See the [Cargo book documentation][feature-resolver@2.0]
  for more information on the feature.
Rustdoc
-------
- [Rustdoc will now include documentation for methods available
  from _nested_ `Deref` traits.][80653]
- [You can now provide a `--default-theme` flag which sets the
  default theme to use for documentation.][79642]
Various improvements to intra-doc links:
- [You can link to non-path primitives such as `slice`.][80181]
- [You can link to associated items.][74489]
- [You can now include generic parameters when linking to items,
  like `Vec<T>`.][76934]
Misc
----
- [You can now pass `--include-ignored` to tests (e.g. with
  `cargo test -- --include-ignored`) to include testing tests marked
  `#[ignore]`.][80053]
Compatibility Notes
-------------------
- [WASI platforms no longer use the `wasm-bindgen` ABI, and instead
  use the wasm32 ABI.][79998]
- [`rustc` no longer promotes division, modulo and indexing operations
  to `const` that could fail.][80579]
- [The minimum version of glibc for the following platforms has
  been bumped to version 2.31 for the distributed artifacts.][81521]
    - `armv5te-unknown-linux-gnueabi`
    - `sparc64-unknown-linux-gnu`
    - `thumbv7neon-unknown-linux-gnueabihf`
    - `armv7-unknown-linux-gnueabi`
    - `x86_64-unknown-linux-gnux32`
- [`atomic::spin_loop_hint` has been deprecated.][80966] It's
  recommended to use `hint::spin_loop` instead.
Internal Only
-------------
- [Consistently avoid constructing optimized MIR when not doing codegen][80718]
[79135]: rust-lang/rust#79135
[74489]: rust-lang/rust#74489
[76934]: rust-lang/rust#76934
[79570]: rust-lang/rust#79570
[80181]: rust-lang/rust#80181
[79642]: rust-lang/rust#79642
[80945]: rust-lang/rust#80945
[80279]: rust-lang/rust#80279
[80053]: rust-lang/rust#80053
[79502]: rust-lang/rust#79502
[75180]: rust-lang/rust#75180
[79135]: rust-lang/rust#79135
[81521]: rust-lang/rust#81521
[80968]: rust-lang/rust#80968
[80959]: rust-lang/rust#80959
[80718]: rust-lang/rust#80718
[80653]: rust-lang/rust#80653
[80579]: rust-lang/rust#80579
[79998]: rust-lang/rust#79998
[78044]: rust-lang/rust#78044
[81455]: rust-lang/rust#81455
[80764]: rust-lang/rust#80764
[80749]: rust-lang/rust#80749
[80662]: rust-lang/rust#80662
[79134]: rust-lang/rust#79134
[80966]: rust-lang/rust#80966
[cargo/8997]: rust-lang/cargo#8997
[cargo/9112]: rust-lang/cargo#9112
[feature-resolver@2.0]: https://doc.rust-lang.org/nightly/cargo/reference/features.html#feature-resolver-version-2
[`Once::call_once_force`]: https://doc.rust-lang.org/stable/std/sync/struct.Once.html#method.call_once_force
[`sync::OnceState`]: https://doc.rust-lang.org/stable/std/sync/struct.OnceState.html
[`panic::panic_any`]: https://doc.rust-lang.org/stable/std/panic/fn.panic_any.html
[`slice::strip_prefix`]: https://doc.rust-lang.org/stable/std/primitive.slice.html#method.strip_prefix
[`slice::strip_suffix`]: https://doc.rust-lang.org/stable/std/primitive.slice.html#method.strip_prefix
[`Arc::increment_strong_count`]: https://doc.rust-lang.org/nightly/std/sync/struct.Arc.html#method.increment_strong_count
[`Arc::decrement_strong_count`]: https://doc.rust-lang.org/nightly/std/sync/struct.Arc.html#method.decrement_strong_count
[`slice::fill_with`]: https://doc.rust-lang.org/nightly/std/primitive.slice.html#method.fill_with
[`ptr::addr_of!`]: https://doc.rust-lang.org/nightly/std/ptr/macro.addr_of.html
[`ptr::addr_of_mut!`]: https://doc.rust-lang.org/nightly/std/ptr/macro.addr_of_mut.html
[`array::IntoIter`]: https://doc.rust-lang.org/nightly/std/array/struct.IntoIter.html
[`slice::split_inclusive`]: https://doc.rust-lang.org/nightly/std/primitive.slice.html#method.split_inclusive
[`slice::split_inclusive_mut`]: https://doc.rust-lang.org/nightly/std/primitive.slice.html#method.split_inclusive_mut
[`str::split_inclusive`]: https://doc.rust-lang.org/nightly/std/primitive.str.html#method.split_inclusive
[`task::Wake`]: https://doc.rust-lang.org/nightly/std/task/trait.Wake.html
[`Seek::stream_position`]: https://doc.rust-lang.org/nightly/std/io/trait.Seek.html#method.stream_position
[`Peekable::next_if`]: https://doc.rust-lang.org/nightly/std/iter/struct.Peekable.html#method.next_if
[`Peekable::next_if_eq`]: https://doc.rust-lang.org/nightly/std/iter/struct.Peekable.html#method.next_if_eq
[`VecDeque::range`]: https://doc.rust-lang.org/nightly/std/collections/struct.VecDeque.html#method.range
[`VecDeque::range_mut`]: https://doc.rust-lang.org/nightly/std/collections/struct.VecDeque.html#method.range_mut