Enable the -Wundef warning for clang

webrtc/modules/audio_coding/codecs/legacy_encoded_audio_frame_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 "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/audio_coding/acm2/rent_a_codec.h"
 #include "webrtc/modules/audio_coding/codecs/legacy_encoded_audio_frame.h"
 
 namespace webrtc {
 
 using NetEqDecoder = acm2::RentACodec::NetEqDecoder;
 
 class SplitBySamplesTest : public ::testing::TestWithParam<NetEqDecoder> {
  protected:
   virtual void SetUp() {
@@ skipping 138 matching lines @@
                       NetEqDecoder::kDecoderPCM16Bwb,
                       NetEqDecoder::kDecoderPCM16Bswb32kHz,
                       NetEqDecoder::kDecoderPCM16Bswb48kHz,
                       NetEqDecoder::kDecoderPCM16B_2ch,
                       NetEqDecoder::kDecoderPCM16Bwb_2ch,
                       NetEqDecoder::kDecoderPCM16Bswb32kHz_2ch,
                       NetEqDecoder::kDecoderPCM16Bswb48kHz_2ch,
                       NetEqDecoder::kDecoderPCM16B_5ch));
 
 }  // namespace webrtc