Fix CP#34085 - restore sys.platform to 'silverlight' on Silverlight.
Fix CP#34085 - restore sys.platform to 'silverlight' on Silverlight.

IronLanguages/ironpython2,slozier/ironpython2,IronLanguages/ironpython2,slozier/ironpython2,IronLanguages/ironpython2,slozier/ironpython2,slozier/ironpython2,slozier/ironpython2,IronLanguages/ironpython2,slozier/ironpython2,IronLanguages/ironpython2,IronLanguages/ironpython2,IronLanguages/ironpython2,slozier/ironpython2