[Bug libstdc++/104442] atomic<T>::wait incorrectly loops in case of spurious notification when __waiter is shared

[rodgertq at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104442

--- Comment #4 from Thomas Rodgers <rodgertq at gcc dot gnu.org> ---
(In reply to Jonathan Wakely from comment #3)
> Tom submitted
> https://gcc.gnu.org/pipermail/gcc-patches/2022-February/590050.html already,
> which is slightly different.

The primary difference was changing the memory order of the load in _M_do_spin.
I may revert that part of the change and submit it separately, as I've noticed
one other case where I'd like to change it from RELAXED to SEQ_CST.