[Bug libstdc++/120527] Native platform wait on darwin

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120527

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And as noted at https://shift.click/blog/futex-like-apis/ ...

OpenBSD has a futex syscall so might be able to reuse the linux code:
https://man.openbsd.org/futex

FreeBSD has _umtx_op with similar functionality:
https://man.freebsd.org/cgi/man.cgi?query=_umtx_op&apropos=0&sektion=2&manpath=FreeBSD+11-current&format=html

DragonFly has umtx_sleep and umtx_wakeup:
https://man.dragonflybsd.org/?command=umtx&section=2