nptl: Add POSIX-proposed _clock functions to hppa pthread.h

The pthread _clock functions that were recently added to nptl need to be
declared in hppa's pthread.h too. After this change, the function
declaration part of sysdeps/nptl/pthread.h and
sysdeps/unix/sysv/linux/hppa/pthread.h are identical.

	* sysdeps/unix/sysv/linux/hppa/pthread.h: Add declarations of
	functions recently added to sysdeps/nptl/pthread.h:
	pthread_mutex_clocklock, pthread_rwlock_clockrdlock,
	pthread_rwlock_clockwrlock and pthread_cond_clockwait.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>