Despite having__GNUC__ set to 4, the standard library of the latest version ofPCC doesn't have__sync_bool_compare_and_swap(). The simplest solution would be to explicitly exclude it:

#elif defined(__GNUC__) && (__GNUC__ >= 4) && !defined(__PCC__)//                                         ^^^^^^^^^^^^^^^^^^^^

I have a feeling there are other compilers that define__GNUC__ that aren't fully compatible with it (e.g. Clang's function attributes differ). This may bite us later.