Enable the -Wundef warning for clang

webrtc/test/testsupport/packet_reader_unittest.cc

 /*
  *  Copyright (c) 2012 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/test/testsupport/packet_reader.h"
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/test/testsupport/unittest_utils.h"
 
 namespace webrtc {
 namespace test {
 
 class PacketReaderTest: public PacketRelatedTest {
  protected:
   PacketReaderTest() {}
   virtual ~PacketReaderTest() {}
   void SetUp() {
@@ skipping 92 matching lines @@
   uint8_t data[kPacketSizeInBytes];
   uint8_t* data_pointer = data;
   reader_->InitializeReading(data, kDataLengthInBytes, kPacketSizeInBytes);
   EXPECT_EQ(kDataLengthInBytes, reader_->NextPacket(&data_pointer));
   // Do it again to make sure nothing changes
   EXPECT_EQ(kDataLengthInBytes, reader_->NextPacket(&data_pointer));
 }
 
 }  // namespace test
 }  // namespace webrtc