[ORC] Re-add the Windows check that was dropped in r328687.

This check prevents the ORC execution tests from running on Windows (which is
not supported yet).

This should fix the windows bots.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@328706 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed