Only activate SSE2 by default on ia32

R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/432863002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22779 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

build/toolchain.gypi

@@ -460,6 +460,8 @@
           'IntermediateDirectory': '$(OutDir)\\obj\\$(ProjectName)',
           'CharacterSet': '1',
         },
+      }],
+      ['OS=="win" and v8_target_arch=="ia32"', {
         'msvs_settings': {
           'VCCLCompilerTool': {
             # Ensure no surprising artifacts from 80bit double math with x86.