Enable the -Wundef warning for clang

webrtc/base/swap_queue_unittest.cc

 /*
  *  Copyright (c) 2015 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/base/swap_queue.h"
 
 #include <vector>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 
 namespace webrtc {
 
 namespace {
 
 // Test parameter for the basic sample based SwapQueue Tests.
 const size_t kChunkSize = 3;
 
 // Queue item verification function for the vector test.
 bool LengthVerifierFunction(const std::vector<int>& v) {
@@ skipping 190 matching lines @@
   EXPECT_TRUE(queue.Insert(&i));
   i = 43;
   EXPECT_FALSE(queue.Insert(&i));
   EXPECT_EQ(i, 43);
   EXPECT_TRUE(queue.Remove(&i));
   EXPECT_EQ(i, 42);
   EXPECT_FALSE(queue.Remove(&i));
 }
 
 }  // namespace webrtc