Enable the -Wundef warning for clang

webrtc/modules/audio_coding/audio_network_adaptor/controller_manager_unittest.cc

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #include <utility>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/audio_coding/audio_network_adaptor/controller_manager.h"
 #include "webrtc/modules/audio_coding/audio_network_adaptor/mock/mock_controller.h"
 #include "webrtc/system_wrappers/include/clock.h"
 
 namespace webrtc {
 
 using ::testing::NiceMock;
 
 namespace {
 
@@ skipping 160 matching lines @@
                         {kNumControllers - 2, kNumControllers - 1, 0, 1});
   states.simulated_clock->AdvanceTimeMilliseconds(kMinReorderingTimeMs);
   // Then let network metrics move a little towards the other controller.
   CheckControllersOrder(
       &states, rtc::Optional<int>(kBandwidthBps - kMinBandwithChangeBps + 1),
       rtc::Optional<float>(kPacketLossFraction),
       {kNumControllers - 2, kNumControllers - 1, 0, 1});
 }
 
 }  // namespace webrtc