Enable AVX opt for Win builds

libvpx_srcs_x86_64_intrinsics.gypi

 # This file is generated. Do not edit.
 # Copyright (c) 2013 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': 'libvpx_intrinsics_mmx',
       'type': 'static_library',
@@ skipping 94 matching lines @@
       'conditions': [
         ['os_posix==1 and OS!="mac" and OS!="ios"', {
           'cflags!': [ '-mfpu=vfpv3-d16' ],
           'cflags': [ '-mavx2', ],
         }],
         ['OS=="mac" or OS=="ios"', {
           'xcode_settings': {
             'OTHER_CFLAGS': [ '-mavx2', ],
           },
         }],
+        ['OS=="win"', {
+          'msvs_settings': {
+            'VCCLCompilerTool': {
+              'EnableEnhancedInstructionSet': '3', # /arch:AVX
+            },
+          },
+        }],
       ],
     },
   ],
 }