Unify the implementations of WaitForSetEvents and WaitForEventsToReset.
The former deals with the possibility of a race between the timeout and
the predicate while the latter does not. The functions were also
inconsistent in when they would recompute the mask. This patch unifies
the two implementations and make them behave exactly the same modulo the
predicate.
rdar://130562344
87f2c25f3d