x11-servers/xorg-server: patch to utilize CLOCK_MONOTONIC_FAST for the clock

This patches the X server to use CLOCK_MONOTONIC_FAST instead of
CLOCK_MONOTONIC for the clock. This is basically a reintroduction of
r208485 by jkim@ that was removed by accident(?).

Since the X server is fine with the Linux _COARSE clock the accuracy of
the FreeBSD _FAST clock should work too. I have run with this patch for
a long time without ill effects.

PR: 252816
Reviewed by: imp, markj, jkim, mhorne
Approved by: x11