AbsRel depends on unix, but Utility.Path.Windows will be used in some
libraries that are part of the setup-depends, which cannot depend on
unix.
The only reason that AbsRel uses getWorkingDirectory on unix is that
it returns RawFilePath. getCurrentDirectory returns FilePath and so
needs a conversion to RawFilePath. Looks like a newer version of
directory will fix that, by using OsPath, so eventually AbsPath should
be able to switch to using getCurrentDirectory on unix, and then the
small code duplication in this commit won't be needed.
Sponsored-by: Dartmouth College's Datalad project
