Refactor how clang warning flags are set.

third_party/zlib/zlib.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.
 
 {
   'targets': [
     {
       'target_name': 'zlib',
       'type': 'static_library',
       'sources': [
@@ skipping 59 matching lines @@
       ],
       'include_dirs': [
         '.',
         '../..',
       ],
       'direct_dependent_settings': {
         'include_dirs': [
           '.',
         ],
       },
+      'variables': {
+        'clang_warning_flags': [
+          # zlib uses `if ((a == b))` for some reason.
+          '-Wno-parentheses-equality',
+        ],
+      },
       'conditions': [
         ['OS!="win"', {
           'sources!': [
             'contrib/minizip/iowin32.c'
           ],
         }],
         ['OS=="android"', {
           'toolsets': ['target', 'host'],
         }],
         ['OS=="mac" or OS=="ios" or os_bsd==1 or OS=="android"', {
           # Mac, Android and the BSDs don't have fopen64, ftello64, or
           # fseeko64. We use fopen, ftell, and fseek instead on these
           # systems.
           'defines': [
             'USE_FILE32API'
           ],
         }],
-        ['clang==1', {
-          'xcode_settings': {
-            'WARNING_CFLAGS': [
-              # zlib uses `if ((a == b))` for some reason.
-              '-Wno-parentheses-equality',
-            ],
-          },
-          'cflags': [
-            '-Wno-parentheses-equality',
-          ],
-        }],
       ],
     },
   ],
 }