Trivial tests for <inttypes.h>/<stdlib.h> *abs and *div functions.

Because I want something to copy & paste into the NDK support library test
that's slightly better than taking the address of the function...

Bug: https://github.com/android-ndk/ndk/issues/502
Test: ran tests
Change-Id: If43089d16691d6a4dcf5d972450b14ed85bbca81