Fix fallout from https://codereview.chromium.org/678423002/

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_x86_simd',
       'type': 'static_library',
       'conditions': [
         ['OS!="ios" and (target_arch=="ia32" or target_arch=="x64")', {
-          'cflags' : ["-msse2", "-msse4.2", "-mpclmul"],
+          'cflags' : ['-msse4.2', '-mpclmul'],
           'xcode_settings' : {
-             'OTHER_CFLAGS' : ["-msse4.2", "-mpclmul"],
+             'OTHER_CFLAGS' : ['-msse4.2', '-mpclmul'],
           },
-          'sources' : [ 'crc_folding.c',
-                        'fill_window_sse.c']
+          'sources' : [
+            'crc_folding.c',
+            'fill_window_sse.c',
+          ],
+          'conditions': [
+            ['OS=="win" and clang==1', {
+              'msvs_settings': {
+                'VCCLCompilerTool': {
+                  'AdditionalOptions': [ '-msse4.2', '-mpclmul' ],
+                },
+              },
+            }],
+          ],
         }, {
           'sources' : [ 'simd_stub.c' ],
-        }], ['OS=="android"', {
+        }],
+        ['OS=="android"', {
           'toolsets': ['target', 'host'],
         }],
       ],
     },
     {
       'target_name': 'zlib',
       'type': 'static_library',
       'sources': [
         'adler32.c',
         'compress.c',
@@ skipping 91 matching lines @@
           # fseeko64. We use fopen, ftell, and fseek instead on these
           # systems.
           'defines': [
             'USE_FILE32API'
           ],
         }],
       ],
     },
   ],
 }