CLEANUP: atomic: use the __atomic variant of BTS/BTR on modern compilers

Probably due to the result of an old copy-paste, HA_ATOMIC_BTS/BTR were
still implemented using the __sync_*  builtins instead of the more
modern __atomic_* which allow to specify the memory model. Let's update
this to use the newer there and also implement the relaxed variants
(which are not used for now).
1 file changed