posix: pthread: consider PTHREAD_EXITED state in pthread_create

If a thread is joined using `pthread_join()`, then the
internal state would be set to `PTHREAD_EXITED`.

Previously, `pthread_create()` would only consider pthreads
with internal state `PTHREAD_TERMINATED` as candidates for new
threads. However, that causes a descriptor leak.

We should be able to reuse a single thread an infinite number
of times.

Here, we also consider threads with internal state
`PTHREAD_EXITED` as candiates in `pthread_create()`.

Fixes #47609

Signed-off-by: Christopher Friedt <[email protected]>
(cherry picked from commit da0398d)

Author: Christopher Friedt

lib/posix/pthread.c

@@ -150,7 +150,7 @@ int pthread_create(pthread_t *newthread, const pthread_attr_t *attr,
 	for (pthread_num = 0;
 	    pthread_num < CONFIG_MAX_PTHREAD_COUNT; pthread_num++) {
 		thread = &posix_thread_pool[pthread_num];
-		if (thread->state == PTHREAD_TERMINATED) {
+		if (thread->state == PTHREAD_EXITED || thread->state == PTHREAD_TERMINATED) {
 			thread->state = PTHREAD_JOINABLE;
 			break;
 		}