GLib checks for __sync_bool_compare_and_swap, and requires
__GCC_HAVE_SYNC_COMPARE_AND_SWAP_4 to be defined if the function is available,
except with special cases like Linux armv5.
Extend the existing workaround to unbreak on old gcc versions that implement
__sync_bool_compare_and_swap but don't provide __GCC_HAVE_* macros.