Enable the -Wundef warning for clang

webrtc/modules/rtp_rtcp/source/rtp_format_vp8_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 <memory>
 
-#include "testing/gmock/include/gmock/gmock.h"
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gmock.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/modules/rtp_rtcp/source/rtp_format_vp8.h"
 #include "webrtc/modules/rtp_rtcp/source/rtp_format_vp8_test_helper.h"
 #include "webrtc/typedefs.h"
 
 #define CHECK_ARRAY_SIZE(expected_size, array)                     \
   static_assert(expected_size == sizeof(array) / sizeof(array[0]), \
                 "check array size");
 
 namespace webrtc {
 namespace {
@@ skipping 570 matching lines @@
             input_header.layerSync);
 }
 
 TEST_F(RtpDepacketizerVp8Test, TestEmptyPayload) {
   // Using a wild pointer to crash on accesses from inside the depacketizer.
   uint8_t* garbage_ptr = reinterpret_cast<uint8_t*>(0x4711);
   RtpDepacketizer::ParsedPayload payload;
   EXPECT_FALSE(depacketizer_->Parse(&payload, garbage_ptr, 0));
 }
 }  // namespace webrtc