thread_pthread.c: use container_of

It's easier to read this macro from ccan than open-coding pointer
arithmetic.

thread_pthread.c (ubf_wakeup_all_threads): use container_of

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61573 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

thread_pthread.c

@@ -1226,8 +1226,7 @@ ubf_wakeup_all_threads(void)
     if (!ubf_threads_empty()) {
 	native_mutex_lock(&ubf_list_lock);
 	list_for_each(&ubf_list_head, dat, ubf_list) {
-	    th = (rb_thread_t *)(
-		((char *)dat) - offsetof(rb_thread_t, native_thread_data));
+	    th = container_of(dat, rb_thread_t, native_thread_data);
 	    ubf_wakeup_thread(th);
 	}
 	native_mutex_unlock(&ubf_list_lock);