os: Fix GetTimeInMicros resolution
GetTimeInMillis is called first, which sets clockid to CLOCK_MONOTONIC_COARSE, which is typically much lower resolution than the callers of GetTimeInMicros want.
Prior to a779fda2, GetTimeInMillis and GetTimeInMicros did not share a clockid.
Restore the clockid split to fix the granularity of GetTimeInMicros.
Signed-off-by: Peter Harris email@example.com