crate: annotate unstalbe *LAST constants

[dybucc]

Description

This PR adds documentation. Some symbols are troublesome. They can change upstream. The Rust change is non-breaking. This requires annotating. It requires usage advice. This patch links to it.

Notes

QNX is untouched. Sources were not found. Their SDK sign up is broken.

Solaris is mostly untouched. Sources were not found. Changes include generic symbols. These were sourced from Illumos.

Sources

• FreeBSD manpage detailing how UTXDB_LASTLOGIN is not the type of constant we would want to deprecate.

  https://man.freebsd.org/cgi/man.cgi?query=getutxent&sektion=3

• DragonFlyBSD sources showing how they define a UTX_DB_LASTLOGX symbol but not a UTX_DB_LASTLOG symbol as we do.

  https://github.com/DragonFlyBSD/DragonFlyBSD/blame/59b78e44f96799c5f46fb3d6d616c18d838a75d0/include/utmpx.h#L89

• Android sources showing how they use the NF_*_PRI_LAST in much the same manner as the Linux sources (further below.)

  https://cs.android.com/search?q=NF_BR_PRI_LAST&ss=android%2Fplatform%2Fsuperproject
  https://cs.android.com/search?q=NF_IP_PRI_LAST&sq=&ss=android%2Fplatform%2Fsuperproject
  https://cs.android.com/search?q=NF_IP6_PRI_LAST&sq=&ss=android%2Fplatform%2Fsuperproject

• Linux sources showing the use of NF_*_PRI_LAST constants as trailing enumeration constants defined in terms of large values.

  https://github.com/torvalds/linux/blob/eb3f4b7426cfd2b79d65b7d37155480b32259a11/include/uapi/linux/netfilter_bridge.h#L42
  https://github.com/torvalds/linux/blob/eb3f4b7426cfd2b79d65b7d37155480b32259a11/include/uapi/linux/netfilter_ipv4.h#L44
  https://github.com/torvalds/linux/blob/eb3f4b7426cfd2b79d65b7d37155480b32259a11/include/uapi/linux/netfilter_ipv6.h#L47

• Illumos sources showing how _PC_LAST should be changed when adding new _PC constants.

  https://github.com/illumos/illumos-gate/blob/7124a0cccb6ebf2bcffdab36f9bdf8fe4c23d77f/usr/src/uts/common/sys/unistd.h#L336

• OpenBSD sources showing how _LC_LAST serves as the "end" value for constants defined prior to it.

  https://github.com/search?q=repo%3Aopenbsd%2Fsrc%20_lc_last&type=code

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 a NetBSD-like module

cc @semarie

Some changes occurred in an OpenBSD module

cc @semarie

Some changes occurred in a solarish module

cc @jclulow, @pfmooney

Some changes occurred in an Android module

cc @maurer

[dybucc]

CI actually passes. There seems to be an issue with a glob import that is not used, but this has not
been changed in the patch (it's not even part of it, for that matter.) For some reason, rebasing
onto main with dependabot updates has ended up with a warning across all of my open PRs due to
that one (now apparently unused) import.

[tgross35]

For updating doc comments like the others, @rustbot author

[rustbot]

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

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[dybucc]

@tgross35 The PR is updated. The description has changed. It should be clearer now.

@rustbot ready