openbsd: add devname(3)

[tobhe]

Description

I'm planning to add OpenBSD support to the drm crate, for that I need devname(3) to replace devname_r which is used on FreeBSD but not available on OpenBSD.

Sources

https://man.openbsd.org/devname.3
https://github.com/openbsd/src/blob/master/include/stdlib.h#L283
https://github.com/openbsd/src/blob/master/lib/libc/gen/devname.c#L73

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]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @tgross35 (or someone else) some time within the next two weeks.

Please see the contribution instructions for more information. Namely, in order to ensure the minimum review times lag, PR authors and assigned reviewers should ensure that the review label (S-waiting-on-review and S-waiting-on-author) stays updated, invoking these commands when appropriate:

• @rustbot author: the review is finished, PR author should check the comments and take action accordingly
• @rustbot review: the author is ready for a review, this PR will be queued again in the reviewer's queue

[rustbot]

Some changes occurred in OpenBSD module

cc @semarie

[semarie]

LGTM. thanks

[tgross35]

Awesome, thank you!