Enable -Wextra-tokens on win clang.

third_party/iaccessible2/iaccessible2.gyp

 # 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.
 
 {
   'variables': {
     'midl_out_dir': '<(SHARED_INTERMEDIATE_DIR)/third_party/iaccessible2',
   },
   'targets': [
     {
       'target_name': 'iaccessible2',
       'type': 'static_library',
+      'variables': {
+        'clang_warning_flags': [
+          # MIDL generates code like "#endif !_MIDL_USE_GUIDDEF_"
+          '-Wno-extra-tokens',
+        ],
+      },
       'sources': [
         'ia2_api_all.idl',
         '<(midl_out_dir)/ia2_api_all.h',
         '<(midl_out_dir)/ia2_api_all_i.c',
       ],
       'hard_dependency': 1,
       'msvs_settings': {
         'VCMIDLTool': {
           'OutputDirectory': '<(midl_out_dir)',
           'DLLDataFileName': 'dlldata.c',
@@ skipping 21 matching lines @@
         ],
       },
       'variables': {
         'clang_warning_flags': [
           '-Wno-incompatible-pointer-types',
         ]
       },
     },
   ],
 }