fsmonitor: use pthread_cond_timedwait for cookie wait

fsmonitor: use pthread_cond_timedwait for cookie wait

The cookie wait in with_lock__wait_for_cookie() uses an infinite
pthread_cond_wait() loop.  The existing comment notes the desire
to switch to pthread_cond_timedwait(), but the routine was not
available in git thread-utils.

On certain container or overlay filesystems, inotify watches may
succeed but events are never delivered.  In this case the daemon
would hang indefinitely waiting for the cookie event, which in
turn causes the client to hang.

Replace the infinite wait with a one-second timeout using
pthread_cond_timedwait().  If the timeout fires, report an
error and let the client proceed with a trivial (full-scan)
response rather than blocking forever.

Signed-off-by: Paul Tarjan <github@paulisageek.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>