A fix for annoying clang error "unused-const-variabl" in third_party code.

gyp/libwebp.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': {
     'use_system_libwebp%': 0,
   },
   'conditions': [
     ['use_system_libwebp==0', {
@@ skipping 94 matching lines @@
             '../third_party/externals/libwebp/src/enc/iterator.c',
             '../third_party/externals/libwebp/src/enc/layer.c',
             '../third_party/externals/libwebp/src/enc/picture.c',
             '../third_party/externals/libwebp/src/enc/quant.c',
             '../third_party/externals/libwebp/src/enc/syntax.c',
             '../third_party/externals/libwebp/src/enc/token.c',
             '../third_party/externals/libwebp/src/enc/tree.c',
             '../third_party/externals/libwebp/src/enc/vp8l.c',
             '../third_party/externals/libwebp/src/enc/webpenc.c',
           ],
+          'cflags': [ '-w' ],
         },
         {
           'target_name': 'libwebp_utils',
           'type': 'static_library',
           'include_dirs': [
               '../third_party/externals/libwebp',
           ],
           'sources': [
             '../third_party/externals/libwebp/src/utils/bit_reader.c',
             '../third_party/externals/libwebp/src/utils/bit_writer.c',
@@ skipping 42 matching lines @@
           'link_settings': {
             'libraries': [
               '-lwebp',
             ],
           },
         }
       ],
     }],
   ],
 }