Fix to build sdch target under clang.

tools/gn/secondary/sdch/BUILD.gn

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 config("sdch_config") {
   include_dirs = [ "open-vcdiff/src" ]
 }
 
 static_library("sdch") {
   sources = [
@@ skipping 34 matching lines @@
     include_dirs = [ "linux" ]
   } else if (is_ios) {
     include_dirs = [ "ios" ]
   } else if (is_mac) {
     include_dirs = [ "mac" ]
   } else if (is_win) {
     include_dirs = [ "win" ]
   }
 
   deps = [ "//third_party/zlib" ]
+
+  if (is_clang) {
+    cflags = [
+      # TODO(mostynb): remove this if open-vcdiff is ever updated for c++11:
+      "-Wno-deprecated-declarations",
+    ]
+  }
 }