fix some semaphore wait semantics (race condition deadlock and error checking)

src/thread/sem_timedwait.c

@@ -8,7 +8,12 @@ int sem_timedwait(sem_t *sem, const struct timespec *at)
 	for (;;) {
 		if (a_fetch_add(sem->__val, -1) > 0) return 0;
 		val = a_fetch_add(sem->__val, 1)+1;
+		if (val==1) __wake(sem->__val, 1, 0);
 		CANCELPT_BEGIN;
+		if (at && at->tv_nsec >= 1000000000UL) {
+			errno = EINVAL;
+			return -1;
+		}
 		if (val <= 0 && __timedwait(sem->__val, val, CLOCK_REALTIME, at, 0) == ETIMEDOUT) {
 			errno = ETIMEDOUT;
 			return -1;

src/thread/sem_trywait.c

@@ -5,7 +5,8 @@ int sem_trywait(sem_t *sem)
 {
 	int val = a_fetch_add(sem->__val, -1);
 	if (val > 0) return 0;
-	a_inc(sem->__val);
+	if (!a_fetch_add(sem->__val, 1))
+		__wake(sem->__val, 1, 0);
 	errno = EAGAIN;
 	return -1;
 }