Use the correct AVX flags for Windows builds

libvpx_srcs_x86_64_intrinsics.gypi

 # This file is generated. Do not edit.
 # Copyright (c) 2014 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 48 matching lines @@
         '<(libvpx_source)/vp8/encoder/x86/quantize_ssse3.c',
         '<(libvpx_source)/vp9/common/x86/vp9_idct_intrin_ssse3.c',
         '<(libvpx_source)/vp9/common/x86/vp9_subpixel_8t_intrin_ssse3.c',
         '<(libvpx_source)/vp9/encoder/x86/vp9_dct_ssse3.c',
       ],
       'cflags': [ '-mssse3', ],
       'xcode_settings': { 'OTHER_CFLAGS': [ '-mssse3' ] },
       'conditions': [
         ['OS=="win" and clang==1', {
           # cl.exe's /arch flag doesn't have a setting for SSSE3/4, and cl.exe
-          # doesn't need it for intrinsics. clang-cl does need it, though.
+          # doesn't need it for intrinsics. There is an /arch flag for AVX2 but
+          # clang-cl needs its own in the form of -mOPT.
           'msvs_settings': {
             'VCCLCompilerTool': { 'AdditionalOptions': [ '-mssse3' ] },
           },
         }],
       ],
     },
     {
       'target_name': 'libvpx_intrinsics_sse4_1',
       'type': 'static_library',
       'include_dirs': [
         'source/config/<(OS_CATEGORY)/<(target_arch_full)',
         '<(libvpx_source)',
       ],
       'sources': [
         '<(libvpx_source)/vp8/encoder/x86/quantize_sse4.c',
       ],
       'cflags': [ '-msse4.1', ],
       'xcode_settings': { 'OTHER_CFLAGS': [ '-msse4.1' ] },
       'conditions': [
         ['OS=="win" and clang==1', {
           # cl.exe's /arch flag doesn't have a setting for SSSE3/4, and cl.exe
-          # doesn't need it for intrinsics. clang-cl does need it, though.
+          # doesn't need it for intrinsics. There is an /arch flag for AVX2 but
+          # clang-cl needs its own in the form of -mOPT.
           'msvs_settings': {
             'VCCLCompilerTool': { 'AdditionalOptions': [ '-msse4.1' ] },
           },
         }],
       ],
     },
     {
       'target_name': 'libvpx_intrinsics_avx2',
       'type': 'static_library',
       'include_dirs': [
@@ skipping 12 matching lines @@
         '<(libvpx_source)/vp9/encoder/x86/vp9_variance_avx2.c',
         '<(libvpx_source)/vp9/encoder/x86/vp9_variance_impl_intrin_avx2.c',
       ],
       'cflags': [ '-mavx2', ],
       'xcode_settings': { 'OTHER_CFLAGS': [ '-mavx2' ] },
       'msvs_settings': {
         'VCCLCompilerTool': {
           'EnableEnhancedInstructionSet': '3', # /arch:AVX
         },
       },
+      'conditions': [
+        ['OS=="win" and clang==1', {
+          # cl.exe's /arch flag doesn't have a setting for SSSE3/4, and cl.exe
+          # doesn't need it for intrinsics. There is an /arch flag for AVX2 but
+          # clang-cl needs its own in the form of -mOPT.
+          'msvs_settings': {
+            'VCCLCompilerTool': { 'AdditionalOptions': [ '-mavx2' ] },
+          },
+        }],
+      ],
     },
   ],
 }