Fix bugzilla issue 24517: druntime tests crash on FreeBSD 14

[jmdavis]

FreeBSD 14 changed the signature of qsort_r to be POSIX-compliant with POSIX, making it so that our binding for it no longer matches, resulting in a crash when it's used.

This implements a fix similar to what the FreeBSD headers do to avoid breaking code (they provide a static inline extern(C++) overload for the old signature). This provides a deprecated extern(D) overload for the old signature. The extern(C) overload now matches the new signature. The changes have been versioned so that they only affect FreeBSD 14 and newer.

Technically, if someone used Cmp when declaring their function for qsort_r, this would still break them (though with a compilation error that should be easy to fix rather than silent breakage or a crash), but I don't really see a way around that, and Cmp is not part of the POSIX API, so no one would have a clue that it was a thing without digging through the bindings. Arguably, we should make it private, since it's not part of POSIX, but I haven't done anything with that in this commit. My guess is that in reality, no D programs are both written to use qsort_r and run on FreeBSD (outside of the druntime tests), but this way, they won't break unless they use Cmp to declare their comparator function. They'll just get a deprecation message that they should update their code.

Regardless, we have to change the signature for FreeBSD 14 for it to work, and this does that.

[dlang-bot]

Thanks for your pull request, @jmdavis!

Bugzilla references

Auto-close	Bugzilla	Severity	Description
✓	24517	normal	druntime tests fail on FreeBSD 14

Testing this PR locally

If you don't have a local development environment setup, you can use Digger to test this PR:

dub run digger -- build "master + dmd#16405"