OpenBSD: add ppoll

[kotauskas]

Description

Moves the ppoll declaration from netbsd/mod.rs to netbsdlike/mod.rs, as OpenBSD has also had ppoll since 5.4.

Sources

Has been around since April 2013.

PSA for others linking to OpenBSD sources: CVSWeb will look fine on your end but will redirect your friends to localhost because their IP address is different from the one with which the link was obtained. Do not bother with it and just link to the GitHub mirror.

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

@rustbot label +stable-nominated

[rustbot]

Some changes occurred in an OpenBSD module

cc @semarie

Some changes occurred in a NetBSD-like module

cc @semarie

[JohnTitor]

Thanks!
LGTM as long as the target maintainer confirms it

[semarie]

LGTM too. thanks