Enable the -Wundef warning for clang

webrtc/modules/audio_coding/neteq/nack_tracker_unittest.cc

 /*
  *  Copyright (c) 2013 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 "webrtc/modules/audio_coding/neteq/nack_tracker.h"
 
 #include <stdint.h>
 
 #include <algorithm>
 #include <memory>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/typedefs.h"
 #include "webrtc/modules/audio_coding/include/audio_coding_module_typedefs.h"
 
 namespace webrtc {
 namespace {
 
 const int kNackThreshold = 3;
 const int kSampleRateHz = 16000;
 const int kPacketSizeMs = 30;
 const uint32_t kTimestampIncrement = 480;  // 30 ms.
@@ skipping 445 matching lines @@
   // sequence number:  1,  2,  3,   4,   5
   // time-to-play:    20, 50, 80, 110, 140
   //
   std::vector<uint16_t> nack_list = nack->GetNackList(100);
   ASSERT_EQ(2u, nack_list.size());
   EXPECT_EQ(4, nack_list[0]);
   EXPECT_EQ(5, nack_list[1]);
 }
 
 }  // namespace webrtc