Refactor how clang warning flags are set.

third_party/libxslt/libxslt.gyp

 # Copyright (c) 2009 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': {
     'conditions': [
       ['os_posix == 1 and OS != "mac"', {
         'os_include': 'linux'
       }],
@@ skipping 88 matching lines @@
             '../libxml/libxml.gyp:libxml',
           ],
           'direct_dependent_settings': {
             'defines': [
               'LIBXSLT_STATIC',
             ],
             'include_dirs': [
               '.',
             ],
           },
+          'variables': {
+            'clang_warning_flags': [
+              # libxslt stores a char[3] in a `const unsigned char*`.
+              '-Wno-pointer-sign',
+            ],
+          },
           'conditions': [
             ['OS!="win"', {'product_name': 'xslt'}],
-            ['clang == 1', {
-              'xcode_settings': {
-                'WARNING_CFLAGS': [
-                  # libxslt stores a char[3] in a `const unsigned char*`.
-                  '-Wno-pointer-sign',
-                ],
-              },
-              'cflags': [
-                '-Wno-pointer-sign',
-              ],
-            }],
           ],
         }],
       ],
     },
   ],
 }