Enable -Wunused-local-typedef

sdch/BUILD.gn

 # Copyright 2014 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 27 matching lines @@
     "open-vcdiff/vsprojects/stdint.h",
   ]
 
   public_configs = [ ":sdch_config" ]
 
   deps = [
     "//base",
     "//third_party/zlib",
   ]
 
+  # gn orders flags on a target before flags from configs. The default config
+  # adds -Wall, and these flags have to be after -Wall -- so they need to come
+  # from a config and can't be on the target directly.
+  config("sdch_warnings") {
+    cflags = []
+    if (is_linux) {
+      # TODO(mostynb): remove this if open-vcdiff is ever updated for c++11:
+      cflags += [ "-Wno-deprecated-declarations" ]
+    }
+
+    if (is_clang) {
+      # sdch uses the pre-c++11 typedef-as-static_assert hack.
+      # https://code.google.com/p/open-vcdiff/issues/detail?id=44
+      cflags += [ "-Wno-unused-local-typedef" ]
+    }
+  }
+  configs += [ ":sdch_warnings" ]
+
   if (is_linux || is_android) {
     include_dirs = [ "linux" ]
   } else if (is_ios) {
     include_dirs = [ "ios" ]
   } else if (is_mac) {
     include_dirs = [ "mac" ]
   } else if (is_win) {
     include_dirs = [ "win" ]
   }
 
   # open-vcdiff's logging.h introduces static initializers. This was
   # reported upstream years ago (
   # https://code.google.com/p/open-vcdiff/issues/detail?id=33 ). Since
   # upstream won't fix this, work around it on the chromium side:
   # Inject a header that forwards to base/logging.h instead (which doesn't
   # introduce static initializers, and which prevents open-vcdiff's
   # logging.h from being used).
   if (is_win) {
     cflags = [
       "/FI", "sdch/logging_forward.h",
     ]
   } else {
     logging_file = rebase_path("logging_forward.h", root_build_dir)
     cflags = [ "-include", logging_file ]
-    if (is_linux) {
-      # TODO(mostynb): remove this if open-vcdiff is ever updated for c++11:
-      cflags += [ "-Wno-deprecated-declarations" ]
-    }
   }
 }