Also add a couple of comments in the tests for ease of understanding
when grepping for `__BIONIC__`.
Bug: N/A
Test: N/A
Change-Id: I7833a3ffbcc3badf9cec95f268d11a6d8a5ff9aa
And fix one thing that this found: apparently <stdlib.h> should also
make the various *WAIT* macros available.
Bug: N/A
Test: builds
Change-Id: Id879bf3c1bddd1170261a809e7280150a74d6b3d