gn: make some warning flags match gyp more closely

build/config/compiler/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.
 
 import("//build/config/android/config.gni")
 if (cpu_arch == "arm") {
   import("//build/config/arm.gni")
 }
 if (is_posix) {
   import("//build/config/gcc/gcc_version.gni")
@@ skipping 682 matching lines @@
 
         # Warns on switches on enums that cover all enum values but
         # also contain a default: branch. Chrome is full of that.
         "-Wno-covered-switch-default",
 
         # Clang considers the `register` keyword as deprecated, but e.g.
         # code generated by flex (used in angle) contains that keyword.
         # http://crbug.com/255186
         "-Wno-deprecated-register",
 
-        # Clang spots more unused functions.
-        "-Wno-unused-function",
+        # TODO(thakis): This used to be implied by -Wno-unused-function,
+        # which we no longer use. Check if it makes sense to remove
+        # this as well. http://crbug.com/316352
+        "-Wno-unneeded-internal-declaration",
       ]
 
       if (!is_mac && !is_ios) {
         cflags_cc += [
           "-Wno-reserved-user-defined-literal",
         ]
       }
     }
     if (gcc_version >= 48) {
       cflags_cc += [
@@ skipping 201 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }