(__atomic_val_bysize, __atomic_bool_bysize): New macros.
(atomic_compare_and_exchange_val_acq): Use it.
(atomic_compare_and_exchange_bool_acq): Likewise.
(atomic_increment_and_test): Invert sense of test.
(atomic_decrement_and_test): Likewise.
* csu/tst-atomic.c: Update those tests to match.