If available, use POSIX unnamed semaphore API to synchronize
parent and child process of onefile application (required for
consistent signal forwarding behavior on non-Windows; see pyinstaller#8900).
The initial implementation used SysV semaphore because POSIX
semaphores turned out to be unavailable on macOS. However, SysV
semaphore API is not available on Termux. Therefore, implement
support for both POSIX and SysV semaphore with preference for
the former. Hopefully this allows us to cover all platforms.

approved these changes Apr 6, 2025

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