Enable the -Wundef warning for clang

webrtc/base/gmock.h

Index: webrtc/base/gmock.h
diff --git a/webrtc/modules/audio_coding/neteq/packet.cc b/webrtc/base/gmock.h
similarity index 64%
copy from webrtc/modules/audio_coding/neteq/packet.cc
copy to webrtc/base/gmock.h
index 8a19fe4d5923d5e22a5b485600c6da0c5f3856ba..2c8014fa1f312de2548d9d5e06e1358b5f8944bc 100644
--- a/webrtc/modules/audio_coding/neteq/packet.cc
+++ b/webrtc/base/gmock.h
@@ -8,12 +8,13 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-#include "webrtc/modules/audio_coding/neteq/packet.h"
+#ifndef WEBRTC_BASE_GMOCK_H_
+#define WEBRTC_BASE_GMOCK_H_
 
-namespace webrtc {
+#include "webrtc/base/ignore_wundef.h"
 
-Packet::Packet() = default;
+RTC_PUSH_IGNORING_WUNDEF()
+#include "testing/gmock/include/gmock/gmock.h"
+RTC_POP_IGNORING_WUNDEF()
 
-Packet::~Packet() = default;
-
-}  // namespace webrtc
+#endif  // WEBRTC_BASE_GMOCK_H_