[jojomodding]

For comparison, in Rust they track down the differences in which flags are ignored in a certain kind of `fcntl` syscall across all the architectures that have this C function, which includes Solaris, Mac OS, the BSDs, Linux, ... This is so that this is correctly handled in Miri, which can then be used to run the test-suite of the OS-specific parts of the standard library, and observe if this uses unsupported features in some way. This ensures that the standard library relies on documented features and not on whatever happens to work right now.

See for example this PR comment: https://github.com/rust-lang/miri/pull/4840#discussion_r2836...