Enable the -Wundef warning for clang

webrtc/modules/utility/source/file_player_unittests.cc

 /*
  *  Copyright (c) 2014 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.
  */
 
 // Unit tests for FilePlayer.
 
 #include "webrtc/modules/utility/include/file_player.h"
 
 #include <stdio.h>
 
 #include <memory>
 #include <string>
 
 #include "gflags/gflags.h"
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/base/md5digest.h"
 #include "webrtc/base/stringencode.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 DEFINE_bool(file_player_output, false, "Generate reference files.");
 
 namespace webrtc {
 
 class FilePlayerTest : public ::testing::Test {
  protected:
@@ skipping 74 matching lines @@
       test::ResourcePath("utility/encapsulated_pcm16b_8khz", "wav");
   // The file is longer than this, but keeping the output shorter limits the
   // runtime for the test.
   const int kOutputLengthMs = 10000;
   const std::string kRefChecksum = "e41d7e1dac8aeae9f21e8e03cd7ecd71";
 
   PlayFileAndCheck(kFileName, kRefChecksum, kOutputLengthMs);
 }
 
 }  // namespace webrtc