[libc++] fix atomic::wait memory order (#146267)
Fixes #109290
See the GH issue for the details. In conclusion, we have two issues in
the `atomic<T>::wait` when `T` does not match our `contention_t`:
- We don't have a total single order which can leads to missed
notification based on the Herd7 simulation on relaxed architectural like
PowerPC
- We assumed the platform wait (`futex_wait`/`__ulock_wait`) has seq_cst
barrier internally but there is no such guarantee
