Attempt to let libvpx's SSE files build with clang-cl.

generate_gypi.sh

Index: generate_gypi.sh
diff --git a/generate_gypi.sh b/generate_gypi.sh
index 09255f193793393ab82ff6b16b75def9dd4d8ee3..156515c48f09d44fe605f1c03d90f61f520d6298 100755
--- a/generate_gypi.sh
+++ b/generate_gypi.sh
@@ -89,6 +89,16 @@ function write_target_definition {
   echo "          'EnableEnhancedInstructionSet': '3', # /arch:AVX" >> $2
   echo "        }," >> $2
   echo "      }," >> $2
+  elif [[ $4 == ssse3 || $4 == sse4.1 ]]; then
+  echo "      'conditions': [" >> $2
+  echo "        ['OS==\"win\" and clang==1', {" >> $2
+  echo "          # cl.exe's /arch flag doesn't have a setting for SSSE3/4, and cl.exe" >> $2
+  echo "          # doesn't need it for intrinsics. clang-cl does need it, though." >> $2
+  echo "          'msvs_settings': {" >> $2
+  echo "            'VCCLCompilerTool': { 'AdditionalOptions': [ '-m$4' ] }," >> $2
+  echo "          }," >> $2
+  echo "        }]," >> $2
+  echo "      ]," >> $2
   fi
   echo "    }," >> $2
 }