nix incantations to build libreboot

i tend to like using Libreboot on the computers of mine that support it - which is many of them, because i have far too many ThinkPads. while setting up Libreboot on a ThinkPad T420, i ran into a SeaBIOS bug - the AHCI initialization code had been recently updated, and it seemed to have broken things... &#x3C;irys> ooh this is fun. seabios commit 8863cbbd15a73b03153553c562f5b1fb939ad4d7 (ahci: add…