tests: posix: pthread: init pthread_attr_t on each iteration

The `test_pthread_descriptor_leak` test was causing a kernel
panic on some platforms. Initially, it was not clear why.

The usual cases were examined - race conditions, stack sizes,
etc. Still no luck.

As it turns out, recycling a thread stack (or at least the
`pthread_attr_t`) in-place does not work on some platforms,
and we need to reinitialize the `pthread_attr_t` and set
set the stack property again prior to calling
`pthread_create()`.

Signed-off-by: Christopher Friedt <[email protected]>
(cherry picked from commit 7c17bda)

Author: Christopher Friedt

tests/posix/common/src/pthread.c

@@ -567,13 +567,12 @@ void test_pthread_descriptor_leak(void)
 	pthread_t pthread1;
 	pthread_attr_t attr;
 
-	zassert_ok(pthread_attr_init(&attr), NULL);
-	zassert_ok(pthread_attr_setstack(&attr, &stack_e[0][0], STACKS), NULL);
-
 	/* If we are leaking descriptors, then this loop will never complete */
 	for (size_t i = 0; i < CONFIG_MAX_PTHREAD_COUNT * 2; ++i) {
-		zassert_ok(pthread_create(&pthread1, &attr, create_thread1, NULL),
+		zassert_equal(0, pthread_attr_init(&attr), NULL);
+		zassert_equal(0, pthread_attr_setstack(&attr, &stack_e[0][0], STACKS), NULL);
+		zassert_equal(0, pthread_create(&pthread1, &attr, create_thread1, NULL),
 			   "unable to create thread %zu", i);
-		zassert_ok(pthread_join(pthread1, &unused), "unable to join thread %zu", i);
+		zassert_equal(0, pthread_join(pthread1, NULL), "unable to join thread %zu", i);
 	}
 }