barrier destroy must also wait for threads in other processes exiting barrier

the vm lock only waits for threads in the same process exiting.
actually this fix is not enough, but it's a start...

src/thread/pthread_barrier_destroy.c

@@ -5,6 +5,8 @@ void __vm_lock(int), __vm_unlock(void);
 int pthread_barrier_destroy(pthread_barrier_t *b)
 {
 	if (b->_b_limit < 0) {
+		int seq = b->_b_seq;
+		if (seq & 1) __wait(&b->_b_seq, 0, seq, 0);
 		__vm_lock(-1);
 		__vm_unlock();
 	}