Fix monotonic clock detection on kFreeBSD

Fix monotonic clock detection on kFreeBSD

Fix monotonic clock detection on kFreeBSD at configure time. This will finally
enable it in QElapsedTimer.

QProcess::waitForFinished() and all other qt_safe_select() users cannot safely
operate without monotonic clock because qt_safe_select() will indicate timeout
earlier than it is supposed when underlying select() call is interrupted
(errno=EINTR).

Gbp-Pq: Name kfreebsd_monotonic_clock.diff