[compiler-rt] Fix atomic_test.c on macOS

The macOS name mangling adds another underscore. Therefore, on macOS
the __atomic_* functions are actually ___atomic_* in libcompiler_rt.dylib.
To handle this case, prepend the asm() argument with __USER_LABEL_PREFIX__
in the same way that atomic.c does.

Reviewed By: ldionne

Differential Revision: https://reviews.llvm.org/D92833

GitOrigin-RevId: 6277bd75dc71ab6cf856ae9a778cab2c90840ca6
1 file changed