Unix: Add sigqueue

[yshui]

Description

Add prototype for sigqueue

Sources

https://github.com/bminor/glibc/blob/8543577b04ded6d979ffcc5a818930e4d74d0645/include/signal.h#L50-L51
https://github.com/bminor/musl/blob/8fd5d031876345e42ae3d11cc07b962f8625bc3b/include/signal.h#L228

Checklist

• Relevant tests in libc-test/semver have been updated
• No placeholder or unstable values like *LAST or *MAX are
  included (see #3131)
• Tested locally (cd libc-test && cargo test --target mytarget);
  especially relevant for platforms that may not be checked in CI

[tgross35]

Please also update the PR description with permalinks to the relevant headers.

[tgross35]

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[yshui]

@rustbot ready

[tgross35]

One more thing, from the PR template:

>     * [ ]  Relevant tests in `libc-test/semver` have been updated

[tgross35]

Looking into this more, I'm not seeing this for OpenBSD or for Android. I don't think it's a safe assumption that this is available on all Unix platforms except Apple and emscripten.

So, please add one definition in src/unix/bsd that excludes target_vendor = "apple", and add one in src/unix/linux_like/linux. Then the semver files freebsd.txt, linux.txt, and netbsd.txt should be updated.

[yshui]

kinda in a weird situation:

android has it.
illumos seems to have it. (can't find the header, though)
cygwin has it.
redox has it, IIUC
qnx neutrino has it
aix has it
haiku has it

i think openbsd and hurd are the ones that don't have it.

[yshui]

and sigqueue is POSIX.1-2001, not an os-specific extension