Enable the -Wundef warning for clang

webrtc/modules/utility/source/audio_frame_operations_unittest.cc

 /*
  *  Copyright (c) 2012 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 "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 #include "webrtc/modules/include/module_common_types.h"
 #include "webrtc/modules/utility/include/audio_frame_operations.h"
 #include "webrtc/base/checks.h"
 
 namespace webrtc {
 namespace {
 
 class AudioFrameOperationsTest : public ::testing::Test {
  protected:
@@ skipping 339 matching lines @@
 
   AudioFrame scaled_frame;
   scaled_frame.samples_per_channel_ = 320;
   scaled_frame.num_channels_ = 1;
   SetFrameData(&scaled_frame, 2);
   VerifyFramesAreEqual(scaled_frame, frame_);
 }
 
 }  // namespace
 }  // namespace webrtc