bpo-41710: PyThread_acquire_lock_timed() uses sem_clockwait() (GH-28671) (GH-28683)

bpo-41710: PyThread_acquire_lock_timed() uses sem_clockwait() (GH-28671) (GH-28683)

On Unix, if the sem_clockwait() function is available in the C
library (glibc 2.30 and newer), the threading.Lock.acquire() method
now uses the monotonic clock (time.CLOCK_MONOTONIC) for the timeout,
rather than using the system clock (time.CLOCK_REALTIME), to not be
affected by system clock changes.

configure now checks if the sem_clockwait() function is available.
(cherry picked from commit 6df8c327532627d6a99991993c52e8e4a9b34968)

Co-authored-by: Victor Stinner <vstinner@python.org>