Enable the -Wundef warning for clang

webrtc/modules/audio_coding/test/PacketLossTest.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.
  */
 
 #include "webrtc/modules/audio_coding/test/PacketLossTest.h"
 
 #include <memory>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/test/testsupport/fileutils.h"
 
 namespace webrtc {
 
 ReceiverWithPacketLoss::ReceiverWithPacketLoss()
     : loss_rate_(0),
       burst_length_(1),
       packet_counter_(0),
       lost_packet_counter_(0),
       burst_lost_counter_(burst_length_) {
@@ skipping 133 matching lines @@
 
   receiver_->Setup(acm.get(), &rtpFile, "packetLoss_out", channels_,
                    actual_loss_rate_, burst_length_);
   receiver_->Run();
   receiver_->Teardown();
   rtpFile.Close();
 #endif
 }
 
 }  // namespace webrtc