nptl: Add POSIX-proposed pthread_cond_clockwait

nptl: Add POSIX-proposed pthread_cond_clockwait

Add:

 int pthread_cond_clockwait (pthread_cond_t *cond,
                             pthread_mutex_t *mutex,
                             clockid_t clockid,
                             const struct timespec *abstime)

which behaves just like pthread_cond_timedwait except it always measures
abstime against the supplied clockid. Currently supports CLOCK_REALTIME
and
CLOCK_MONOTONIC and returns EINVAL if any other clock is specified.

Includes feedback from many others. This function was originally
proposed[1] as pthread_cond_timedwaitonclock_np, but The Austin Group
preferred the new name.

	* nptl/Makefile: Add tst-cond26 and tst-cond27
	* nptl/Versions (GLIBC_2.30): Add pthread_cond_clockwait
	* sysdeps/nptl/pthread.h: Likewise
	* nptl/forward.c: Add __pthread_cond_clockwait
	* nptl/forward.c: Likewise
	* nptl/pthreadP.h: Likewise
	* sysdeps/nptl/pthread-functions.h: Likewise
	* nptl/pthread_cond_wait.c (__pthread_cond_wait_common): Add
	clockid parameter and comment describing why we don't need to
	check
	its value. Use that value when calling
	futex_abstimed_wait_cancelable rather than reading the clock
	from
	the flags. (__pthread_cond_wait): Pass unused clockid parameter.
	(__pthread_cond_timedwait): Read clock from flags and pass it to
	__pthread_cond_wait_common. (__pthread_cond_clockwait): Add new
	function with weak alias from pthread_cond_clockwait.
	* sysdeps/mach/hurd/i386/libpthread.abilist (GLIBC_2.30):
	* Likewise.
	* sysdeps/unix/sysv/linux/aarch64/libpthread.abilist
	* (GLIBC_2.30): Likewise.
	* sysdeps/unix/sysv/linux/alpha/libpthread.abilist (GLIBC_2.30):
	* Likewise.
	* sysdeps/unix/sysv/linux/arm/libpthread.abilist (GLIBC_2.30):
	* Likewise.
	* sysdeps/unix/sysv/linux/csky/libpthread.abilist (GLIBC_2.30):
	* Likewise.
	* sysdeps/unix/sysv/linux/hppa/libpthread.abilist (GLIBC_2.30):
	* Likewise.
	* sysdeps/unix/sysv/linux/i386/libpthread.abilist (GLIBC_2.30):
	* Likewise.
	* sysdeps/unix/sysv/linux/ia64/libpthread.abilist (GLIBC_2.30):
	* Likewise.
	* sysdeps/unix/sysv/linux/m68k/coldfire/libpthread.abilist
	(GLIBC_2.30): Likewise.
	* sysdeps/unix/sysv/linux/m68k/m680x0/libpthread.abilist
	(GLIBC_2.30): Likewise.
	* sysdeps/unix/sysv/linux/microblaze/libpthread.abilist
	(GLIBC_2.30): Likewise.
	* sysdeps/unix/sysv/linux/mips/mips32/libpthread.abilist
	(GLIBC_2.30): Likewise.
	* sysdeps/unix/sysv/linux/mips/mips64/libpthread.abilist
	(GLIBC_2.30): Likewise.
	* sysdeps/unix/sysv/linux/nios2/libpthread.abilist (GLIBC_2.30):
	* Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc32/libpthread.abilist
	(GLIBC_2.30): Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/be/libpthread.abilist
	(GLIBC_2.30): Likewise.
	* sysdeps/unix/sysv/linux/powerpc/powerpc64/le/libpthread.abilist
	(GLIBC_2.30): Likewise.
	* sysdeps/unix/sysv/linux/riscv/rv64/libpthread.abilist
	(GLIBC_2.30): Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-32/libpthread.abilist
	(GLIBC_2.30): Likewise.
	* sysdeps/unix/sysv/linux/s390/s390-64/libpthread.abilist
	(GLIBC_2.30): Likewise.
	* sysdeps/unix/sysv/linux/sh/libpthread.abilist (GLIBC_2.30):
	* Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc32/libpthread.abilist
	(GLIBC_2.30): Likewise.
	* sysdeps/unix/sysv/linux/sparc/sparc64/libpthread.abilist
	(GLIBC_2.30): Likewise.
	* sysdeps/unix/sysv/linux/x86_64/64/libpthread.abilist
	(GLIBC_2.30): Likewise.
	* sysdeps/unix/sysv/linux/x86_64/x32/libpthread.abilist
	(GLIBC_2.30): Likewise.
	* nptl/tst-cond11.c (run_test): Support testing
	pthread_cond_clockwait too by using a special magic
	CLOCK_USE_ATTR_CLOCK value to determine whether to call
	pthread_cond_timedwait or pthread_cond_clockwait. (do_test):
	Pass
	CLOCK_USE_ATTR_CLOCK for existing tests, and add new tests using
	all combinations of CLOCK_MONOTONIC and CLOCK_REALTIME.
	* ntpl/tst-cond26.c: New test for passing unsupported and
	* invalid
	clocks to pthread_cond_clockwait.
	* nptl/tst-cond27.c: Add test similar to tst-cond5.c, but using
	struct timespec and pthread_cond_clockwait.
	* manual/threads.texi: Document pthread_cond_clockwait. The
	* comment
	was provided by Carlos O'Donell.

[1] https://sourceware.org/ml/libc-alpha/2015-07/msg00193.html

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