Relax definitions.test to accept windows file paths. Reviewers: ilya-biryukov Subscribers: cfe-commits Differential Revision: https://reviews.llvm.org/D39797 git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@317692 91177308-0d34-0410-b5e6-96231b3b80d8