Enable the -Wundef warning for clang

webrtc/modules/audio_coding/codecs/ilbc/ilbc_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/codecs/ilbc/audio_decoder_ilbc.h"
 #include "webrtc/modules/audio_coding/codecs/ilbc/audio_encoder_ilbc.h"
 #include "webrtc/modules/audio_coding/codecs/legacy_encoded_audio_frame.h"
 
 namespace webrtc {
 
 TEST(IlbcTest, BadPacket) {
   // Get a good packet.
   AudioEncoderIlbc::Config config;
   config.frame_size_ms = 20;  // We need 20 ms rather than the default 30 ms;
@@ skipping 108 matching lines @@
 // Payload not an integer number of frames.
 TEST(IlbcTest, SplitUnevenPayload) {
   AudioDecoderIlbc decoder;
   constexpr size_t kPayloadLengthBytes = 39;  // Not an even number of frames.
   const auto results =
       decoder.ParsePayload(rtc::Buffer(kPayloadLengthBytes), 0);
   EXPECT_TRUE(results.empty());
 }
 
 }  // namespace webrtc