lit.py: Previous test fix was a red herring; backslashes are escapes

I don't have access to a Windows machine at the moment, so if this
doesn't fix it I'll just revert for now.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@315782 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed