Fixes stdatomic.h test to match C11 spec

C11 defines the expected value to atomic_compare_exchange_* as being non-atomic
types. Using an atomic type is a syntax error in clang.

http://en.cppreference.com/w/c/atomic/atomic_compare_exchange

Change-Id: I74de1061fa1fc50d835451792d902000f368200e
1 file changed