winpthreads: Increase precision of CLOCK_REALTIME, add CLOCK_REALTIME_COARSE. Use GetSystemTimePreciseAsFileTime() for CLOCK_REALTIME if available. Always use GetSystemTimeAsFileTime() for CLOCK_REALTIME_COARSE. Signed-off-by: Christian Franke <christian.franke@t-online.de> Signed-off-by: Liu Hao <lh_mouse@126.com>