Stop checking the global thread list in several trivial cases.

Since removing the global thread is hard, let's take the different
groups of functions individually.

The existing code was racy anyway, because the thread might still be
on the list but have exited (leaving tid == 0).

Bug: http://b/19636317
Test: ran tests
Change-Id: Icc0986ff124d5f9b8a653edf718c549d1563973b