suppress masked cancellation in pthread_join

like close, pthread_join is a resource-deallocation function which is
also a cancellation point. the intent of masked cancellation mode is
to exempt such functions from failure with ECANCELED.

src/thread/pthread_join.c

@@ -3,12 +3,16 @@
 
 int __munmap(void *, size_t);
 void __pthread_testcancel(void);
+int __pthread_setcancelstate(int, int *);
 
 int __pthread_join(pthread_t t, void **res)
 {
-	int tmp;
+	int tmp, cs;
 	__pthread_testcancel();
+	__pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
+	if (cs == PTHREAD_CANCEL_ENABLE) __pthread_setcancelstate(cs, 0);
 	while ((tmp = t->tid)) __timedwait_cp(&t->tid, tmp, 0, 0, 0);
+	__pthread_setcancelstate(cs, 0);
 	if (res) *res = t->result;
 	if (t->map_base) __munmap(t->map_base, t->map_size);
 	return 0;