macOS: Use clock_gettime_nsec_np() for omrtime_hires_clock()

[knn-k]

This commit changes the implementation of omrtime_hires_clock() for
macOS.

Signed-off-by: KONNO Kazuhiro konno@jp.ibm.com

[knn-k]

See eclipse-openj9/openj9#14636 (comment) for the background.

This commit implements monotonic omrtime_hires_clock() for macOS. Apple's document (https://developer.apple.com/documentation/kernel/1646199-mach_continuous_time) mentions clock_gettime_nsec_np(CLOCK_MONOTONIC_RAW). It returns __uint64_t.

There is a design choice here: Should omrtime_hires_clock() return nanoseconds or microseconds (as it does for other UNIXes)?

[knn-k]

I merged my own PR by mistake.
Reverting by #6569.

[dmitripivkine]

There is a design choice here: Should omrtime_hires_clock() return nanoseconds or microseconds (as it does for other UNIXes)?

The resolution of returned clock is hardcoded in OMRTIME_HIRES_CLOCK_FREQUENCY. It makes omrtime_hires_delta() work properly. In the case resolution of omrtime_hires_clock() return is going to be changed to nanoseconds this constant should be redefined accordingly