libstdc++: Fix std::future::wait_until for subsecond negative times [PR118093]

libstdc++: Fix std::future::wait_until for subsecond negative times [PR118093]

The current check for negative times (i.e. before the epoch) only checks
for a negative number of seconds. For a time 1ms before the epoch the
seconds part will be zero, but the futex syscall will still fail with an
EINVAL error. Extend the check to handle this case.

This change adds a redundant check in the headers too, so that we avoid
even calling into the library for negative times. Both checks can be
marked [[unlikely]]. The check in the headers avoids the cost of
splitting the time into seconds and nanoseconds and then making a PLT
call. The check inside the library matches where we were checking
already, and fixes existing binaries that were compiled against older
headers but use a newer libstdc++.so.6 at runtime.

libstdc++-v3/ChangeLog:

	PR libstdc++/118093
	* include/bits/atomic_futex.h (_M_load_and_test_until_impl):
	Return false for times before the epoch.
	* src/c++11/futex.cc (_M_futex_wait_until): Extend check for
	negative times to check for subsecond times. Add unlikely
	attribute.
	(_M_futex_wait_until_steady): Likewise.
	* testsuite/30_threads/future/members/118093.cc: New test.