Enable the -Wundef warning for clang

webrtc/base/httpclient.h

 /*
  *  Copyright 2004 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.
  */
 
@@ skipping 33 matching lines @@
 //////////////////////////////////////////////////////////////////////
 
 class DiskCache;
 class HttpClient;
 class IPNetPool;
 
 class SignalThread;
 // What to do:  Define STRICT_HTTP_ERROR=1 in your makefile.  Use HttpError in
 // your code (HttpErrorType should only be used for code that is shared
 // with groups which have not yet migrated).
-#if STRICT_HTTP_ERROR
+#if defined(STRICT_HTTP_ERROR) && STRICT_HTTP_ERROR
 typedef HttpError HttpErrorType;
 #else  // !STRICT_HTTP_ERROR
 typedef int HttpErrorType;
 #endif  // !STRICT_HTTP_ERROR
 
 class HttpClient : private IHttpNotify, public sigslot::has_slots<> {
 public:
   // If HttpRequestData and HttpResponseData objects are provided, they must
   // be freed by the caller.  Otherwise, an internal object is allocated.
   HttpClient(const std::string& agent, StreamPool* pool,
@@ skipping 122 matching lines @@
 public:
   HttpClientDefault(SocketFactory* factory, const std::string& agent,
                     HttpTransaction* transaction = NULL);
 };
 
 //////////////////////////////////////////////////////////////////////
 
 }  // namespace rtc
 
 #endif // WEBRTC_BASE_HTTPCLIENT_H__