fix: supports cross-platform building and 32-bit

[YumeYuka]

Commit By @ShIroRRen

[ShIroRRen]

Windows does not support stdbuf. cygwin support is enough.

Just to make the if more correct, although it won't build it

[ShIroRRen]

You should add

#[cfg(not(unix))]
compile_error!("stdbuf is not supported on the target");

and remove stdbuf-error-command-not-supported from ftl files instead.

I added it

[oech3]

Does this PR cover #11311 and #11428 ? cc @0323pin

[sylvestre]

plenty of jobs are failing

[ShIroRRen]

plenty of jobs are failing

Because of the feature, I missed one during testing, and now I've added it.

[github-actions]

GNU testsuite comparison:

Congrats! The gnu test tests/printf/printf-surprise is now passing!
Note: The gnu test tests/env/env-signal-handler was skipped on 'main' but is now failing.