Enable the -Wundef warning for clang

webrtc/modules/audio_coding/neteq/tools/packet_unittest.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 test Packet class.
 
 #include "webrtc/modules/audio_coding/neteq/tools/packet.h"
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 namespace webrtc {
 namespace test {
 
 namespace {
 const int kHeaderLengthBytes = 12;
 
 void MakeRtpHeader(int payload_type,
                    int seq_number,
                    uint32_t timestamp,
@@ skipping 167 matching lines @@
     }
     EXPECT_EQ(kSsrc, red_block->ssrc);
     EXPECT_EQ(0, red_block->numCSRCs);
     ++block_index;
   }
   Packet::DeleteRedHeaders(&red_headers);
 }
 
 }  // namespace test
 }  // namespace webrtc