hppa: Optimize atomic_compare_and_exchange_val_acq

Changelog:
	* sysdeps/unix/sysv/linux/hppa/atomic-machine.h: Don't include
	abort-instr.h.
	(EFAULT): Remove conditional define.
	(ENOSYS): Likewise.
	(atomic_compare_and_exchange_val_acq): Use instruction nullification
	instead of conditional branch instructions.