Move large part of asan_test_utils.h to sanitizer_common.
Move my_rand() to the common header.

This lets us avoid the use of rand_r in sanitizer_common tests.
There is no rand_r on Android.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@172421 91177308-0d34-0410-b5e6-96231b3b80d8