Revert 159854 "Promote platform exclusion rules to config.gyp."

> Promote platform exclusion rules to config.gyp.
> 
> BUG=None
> TEST=blink_platform_unittests
> R=abarth@chromium.org
> 
> Review URL: https://codereview.chromium.org/27623002

TBR=tfarina@chromium.org

Review URL: https://codereview.chromium.org/27278005

git-svn-id: svn://svn.chromium.org/blink/trunk@159901 bbb929c8-8fbe-4397-9dbb-9b2b20218538