Fix mq_notify pthread_barrier_* namespace (bug 18544).

Fix mq_notify pthread_barrier_* namespace (bug 18544).

mq_notify (present in POSIX by 1996) brings in references to
pthread_barrier_init and pthread_barrier_wait (new in the 2001 edition
of POSIX).  This patch fixes this by making those functions into weak
aliases of __pthread_barrier_*, exporting the __pthread_barrier_*
names at version GLIBC_PRIVATE and using them in mq_notify.

Tested for x86_64 and x86 (testsuite, and comparison of installed
stripped shared libraries).  Changes in addresses from dynamic symbol
table / PLT changes render most comparisons not particularly useful,
but when the addresses of subsequent code don't change there's no sign
of unexpected changes there.  This patch does not remove any
linknamespace XFAILs because of other namespace issues remaining with
mqueue.h functions.

	[BZ #18544]
	* nptl/pthread_barrier_init.c (pthread_barrier_init): Rename to
	__pthread_barrier_init and define as weak alias of
	__pthread_barrier_init.
	* sysdeps/sparc/nptl/pthread_barrier_init.c
	(pthread_barrier_init): Likewise.
	* nptl/pthread_barrier_wait.c (pthread_barrier_wait): Rename to
	__pthread_barrier_wait and define as weak alias of
	__pthread_barrier_wait.
	* sysdeps/sparc/nptl/pthread_barrier_wait.c
	(pthread_barrier_wait): Likewise.
	* sysdeps/sparc/sparc32/pthread_barrier_wait.c
	(pthread_barrier_wait): Likewise.
	* sysdeps/unix/sysv/linux/i386/i486/pthread_barrier_wait.S
	(pthread_barrier_wait): Likewise.
	* sysdeps/unix/sysv/linux/x86_64/pthread_barrier_wait.S
	(pthread_barrier_wait): Likewise.
	* nptl/Versions (libpthread): Export __pthread_barrier_init and
	__pthread_barrier_wait at version GLIBC_PRIVATE.
	* include/pthread.h (__pthread_barrier_init): Declare.
	(__pthread_barrier_wait): Likewise.
	* sysdeps/unix/sysv/linux/mq_notify.c (notification_function):
	Call __pthread_barrier_wait instead of pthread_barrier_wait.
	(helper_thread): Likewise.
	(init_mq_netlink): Call __pthread_barrier_init instead of
	pthread_barrier_init.