Enable the -Wundef warning for clang

webrtc/api/test/mock_webrtcsession.h

 /*
  *  Copyright 2016 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.
  */
 
 #ifndef WEBRTC_API_TEST_MOCK_WEBRTCSESSION_H_
 #define WEBRTC_API_TEST_MOCK_WEBRTCSESSION_H_
 
 #include <memory>
 #include <string>
 
 #include "webrtc/api/webrtcsession.h"
-#include "testing/gmock/include/gmock/gmock.h"
+#include "webrtc/test/gmock.h"
 
 namespace webrtc {
 
 class MockWebRtcSession : public webrtc::WebRtcSession {
  public:
   // TODO(nisse): Valid overrides commented out, because the gmock
   // methods don't use any override declarations, and we want to avoid
   // warnings from -Winconsistent-missing-override. See
   // http://crbug.com/428099.
   explicit MockWebRtcSession(MediaControllerInterface* media_controller)
@@ skipping 24 matching lines @@
     return std::unique_ptr<rtc::SSLCertificate>(
         GetRemoteSSLCertificate_ReturnsRawPointer(transport_name));
   }
   MOCK_METHOD1(GetRemoteSSLCertificate_ReturnsRawPointer,
                rtc::SSLCertificate*(const std::string& transport_name));
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_API_TEST_MOCK_WEBRTCSESSION_H_