Enable the -Wundef warning for clang

webrtc/base/proxydetect.cc

 /*
  *  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 20 matching lines @@
 #include <map>
 #include <memory>
 
 #include "webrtc/base/arraysize.h"
 #include "webrtc/base/fileutils.h"
 #include "webrtc/base/httpcommon.h"
 #include "webrtc/base/httpcommon-inl.h"
 #include "webrtc/base/pathutils.h"
 #include "webrtc/base/stringutils.h"
 
+#define _TRY_JSPROXY 0
+#define _TRY_WM_FINDPROXY 0
+
 #if defined(WEBRTC_WIN)
 #define _TRY_WINHTTP 1
-#define _TRY_JSPROXY 0
-#define _TRY_WM_FINDPROXY 0
 #define _TRY_IE_LAN_SETTINGS 1
+#else
+#define _TRY_WINHTTP 0
+#define _TRY_IE_LAN_SETTINGS 0
 #endif  // WEBRTC_WIN
 
 // For all platforms try Firefox.
 #define _TRY_FIREFOX 1
 
 // Use profiles.ini to find the correct profile for this user.
 // If not set, we'll just look for the default one.
 #define USE_FIREFOX_PROFILES_INI 1
 
 static const size_t kMaxLineLength = 1024;
@@ skipping 1230 matching lines @@
     if (!result) {
       // Either auto detection is not supported or we simply didn't
       // find any proxy, reset type.
       proxy->type = rtc::PROXY_NONE;
     }
   }
   return result;
 }
 
 }  // namespace rtc