freebsd15: Add ki_uerrmsg to struct kinfo_proc

[neuschaefer]

Description

During the development of FreeBSD 15, a field was added to kinfo_proc. With this PR and #4552, the libc-test suite passes on FreeBSD 15 on ppc64.

Sources

Upstream commit: freebsd/freebsd-src@7212b37

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]

@asomers given this does technically break the struct definition, do you want this on stable? I think if this is done, the struct should be marked #[non_exhaustive] at the same time so future similar changes aren't breaking (in 1.0 everything will be #[non_exhaustive]).

The change itself LGTM

[asomers]

This change only affects FreeBSD 15. That release is still under development, and therefore no backwards-compatibility concerns apply. So yes I think we should merge it to libc-0.2.

[tgross35]

Thanks for confirming, that's perfect. I think we should still add #[non_exhaustive] to allow changing padding fields into named fields in the future.