Enable clang warning for ignored attributes.

build/common.gypi

 # Copyright (c) 2012 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 5685 matching lines @@
                 'AdditionalOptions': [
                   # Many files use intrinsics without including this header.
                   # TODO(hans): Fix those files, or move this to sub-GYPs.
                   '/FIIntrin.h',
 
                   # TODO(hans): Make this list shorter eventually, http://crbug.com/504657
                   '-Qunused-arguments',  # http://crbug.com/504658
                   '-Wno-c++11-compat-deprecated-writable-strings',  # http://crbug.com/504659
                   '-Wno-empty-body',  # http://crbug.com/504661
                   '-Wno-extra-tokens',  # http://crbug.com/504663
-                  '-Wno-ignored-attributes',  # http://crbug.com/504695
                   '-Wno-incompatible-pointer-types',  # http://crbug.com/504696
                   '-Wno-int-to-void-pointer-cast',  # http://crbug.com/504697
                   '-Wno-invalid-noreturn',  # http://crbug.com/504698
                   '-Wno-logical-op-parentheses',  # http://crbug.com/504699
                   '-Wno-microsoft',  # http://crbug.com/505296
                   '-Wno-missing-braces',  # http://crbug.com/505297
                   '-Wno-msvc-include',  # http://crbug.com/505299
                   '-Wno-overloaded-virtual',  # http://crbug.com/505301
                   '-Wno-pointer-sign',  # http://crbug.com/505303
                   '-Wno-reorder',  # http://crbug.com/505304
@@ skipping 474 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }