Fix typo list_insert -> list_push_back for thread.child_results

src/threads/thread.c

@@ -264,8 +264,8 @@ thread_create (const char *name, int priority,
   intr_set_level (old_level);
 
   /* No need to synchronise child_results since it is only ever accessed by one
-     thread. */
-  list_insert (&parent_thread->child_results, &t->result->elem);
+     thread. By the nature of increasing TIDs, this list is ordered. */
+  list_push_back (&parent_thread->child_results, &t->result->elem);
 
   /* Add to run queue. */
   thread_unblock (t);