common_timers: define NSEC_PER_SEC as long long to avoid overflow on 32-bit am: 293d07002b am: 13c6ab9c55 am: de2a67c8fd

Original change: https://android-review.googlesource.com/c/platform/external/ltp/+/3543740

Change-Id: Ib68e36432b81486b85ee7c1bd994cf56f04ffc2b
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>