Map performance counter to the appropriate monotonic clock
used by ntdll/unix/sync.c

The performance counter timestamp clock won't be available
under Mac and platforms without clock_gettime.
Signed-off-by: Joshua Ashton <joshua@froggi.es>
Signed-off-by: Liam Middlebrook <lmiddlebrook@nvidia.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>