disabled thread_set_name for OSX (close #568)

src/std/thread.c

@@ -937,6 +937,8 @@ HL_PRIM void hl_thread_set_name( hl_thread *t, const char *name ) {
 	// nothing
 #elif defined(HL_WIN)
 	SetThreadName((DWORD)(int_val)t,name);
+#elif defined(HL_MAC)
+	// pthread_setname_np only possible for current thread
 #else
 	pthread_setname_np((pthread_t)t,name);
 #endif