refactor: deprecate RAND_MAX constant in FreeBSD

[dybucc]

Description

This constant does not seem to have had any changes since a binding was defined in all modules but
the FreeBSD tree.

This deprecation may or may not be worth it, as the only real change was between FreeBSD 12 and
FreeBSD 13.

This type of constant seems like the "delimitter" value mentioned in #3131, so that's why I thought
it could be marked for deprecation.

Sources

• FreeBSD tree in libc where the constant was added to specific FreeBSD releases as it changed
  between FreeBSD 12 and FreeBSD 13.
  https://github.com/rust-lang/libc/blob/main/src/unix/bsd/freebsdlike/freebsd/freebsd15/mod.rs#L323
• C standard library documentation (unofficial) mentioning the purpose of the constant as a "limit"
  value rand.
  https://en.cppreference.com/c/numeric/random/RAND_MAX

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]

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.