Enable -Wunused-local-typedef

sdch/BUILD.gn

Index: sdch/BUILD.gn
diff --git a/sdch/BUILD.gn b/sdch/BUILD.gn
index 7a95f1fa1547c80f49fc416ef7b5b672b34cd7b1..727fb497712a3dfad9efbed989158701c1978a11 100644
--- a/sdch/BUILD.gn
+++ b/sdch/BUILD.gn
@@ -45,6 +45,24 @@ static_library("sdch") {
     "//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) {
@@ -69,9 +87,5 @@ static_library("sdch") {
   } 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" ]
-    }
   }
 }