* sysdeps/unix/sysv/linux/i386/i486/pthread_barrier_wait.S
(pthread_barrier_wait): After wakeup, release lock only when the
last thread stopped using the barrier object.
* sysdeps/unix/sysv/linux/x86_64/pthread_barrier_wait.S
(pthread_barrier_wait): Likewise.
* sysdeps/pthread/pthread_barrier_wait.c (pthread_barrier_wait):
Likewise.
* Makefile (tests): Add tst-barrier4.
* tst-barrier4.c: New file.
