Enable the -Wundef warning for clang

webrtc/media/engine/simulcast_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.
  */
 
 #include <string>
 
-#include "testing/gtest/include/gtest/gtest.h"
+#include "webrtc/test/gtest.h"
 #include "webrtc/media/engine/simulcast.h"
 
 namespace cricket {
 
 class ScreenshareLayerConfigTest : public testing::Test,
                                    protected ScreenshareLayerConfig {
  public:
   ScreenshareLayerConfigTest() : ScreenshareLayerConfig(0, 0) {}
 
   void ExpectParsingFails(const std::string& group) {
@@ skipping 23 matching lines @@
 }
 
 TEST_F(ScreenshareLayerConfigTest, ParsesValidBitrateConfig) {
   ScreenshareLayerConfig config(100, 1000);
   EXPECT_TRUE(ScreenshareLayerConfig::FromFieldTrialGroup("101-1001", &config));
   EXPECT_EQ(101, config.tl0_bitrate_kbps);
   EXPECT_EQ(1001, config.tl1_bitrate_kbps);
 }
 
 }  // namespace cricket