Treat std::atomic_int as a trivial class member when checking for non-trivial classes.

tools/clang/plugins/tests/trivial_ctor.h

+// Copyright (c) 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef TRIVIAL_CTOR_H_
+#define TRIVIAL_CTOR_H_
+
+template<typename T>
+struct atomic {
+/*
+  atomic() noexcept = default;
+  ~atomic() noexcept = default;
+  atomic(const atomic&) = delete;
+  atomic& operator=(const atomic&) = delete;
+  atomic& operator=(const atomic&) volatile = delete;
+
+  constexpr atomic(T i) noexcept : i(i) { }
+*/
+
+  T i;
+};
+
+typedef atomic<int> atomic_int;
+
+struct MySpinLock {
+  MySpinLock();
+  ~MySpinLock();
+  MySpinLock(const MySpinLock&);
+  MySpinLock(MySpinLock&&);
+  atomic_int lock_;
+};
+
+#endif  // TRIVIAL_CTOR_H_