On Aix, thread_cputime and clock_gettime (with CLOCK_THREAD_CPUTIME_ID)
can both be used to get time consumed by a thread. However,
thread_cputime is preferable, as it is has better resolution
(nanoseconds vs 10ms for clock_gettime).

Change-Id: I8a698f85defa011f6ed1eb5f47a6dbd4e21d1f67
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3036281
Commit-Queue: Vasili Skurydzin <vasili.skurydzin@ibm.com>
Reviewed-by: Milad Fa <mfarazma@redhat.com>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75793}