clang-tools-extra/modularize: Compare Paths to Prefix as natively-canonicalized form.

On Win32, paths are not expected to be canonicalized.

git-svn-id: https://llvm.org/svn/llvm-project/clang-tools-extra/trunk@192763 91177308-0d34-0410-b5e6-96231b3b80d8