Revert "Don't cleanup already-detached or exiting/exited threads"

This reverts commit fbcaa9e

Author: kleisauke

system/lib/libc/musl/src/thread/pthread_detach.c

@@ -11,11 +11,7 @@ static int __pthread_detach(pthread_t t)
 	/* If the cas fails, detach state is either already-detached
 	 * or exiting/exited, and pthread_join will trap or cleanup. */
 	if (a_cas(&t->detach_state, DT_JOINABLE, DT_DETACHED) != DT_JOINABLE)
-#ifdef __EMSCRIPTEN__ // XXX Emscripten don't cleanup already-detached or exiting/exited threads
-		return EINVAL;
-#else
 		return __pthread_join(t, 0);
-#endif
 	return 0;
 }