libstdc++: Fix wrong thread waking on notify [PR100334]

libstdc++: Fix wrong thread waking on notify [PR100334]

Fixes https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100334

libstdc++-v3/ChangeLog:
	* include/bits/atomic_wait.h (__waiter::_M_do_wait_v): loop
	until value change observed.
	(__waiter_base::_M_laundered): New member.
	(__waiter_base::_M_notify): Check _M_laundered to determine
	whether to wake one or all.
	(__detail::__atomic_compare): Return true if call to
	__builtin_memcmp() == 0.
	(__waiter_base::_S_do_spin_v): Adjust predicate.
	* testsuite/29_atomics/atomic/wait_notify/100334.cc: New
	test.