luna-package fails to compile on Windows

[mwu-tow]

General Summary

luna-package fails to build on Windows.
Specifically this: https://github.com/luna/luna/blob/master/package/src/Luna/Package.hs#L278 :
Path.mkAbsDir "/" is not legal on Windows, as / is not a valid absolute path.
http://hackage.haskell.org/package/path-0.6.1/docs/Path.html#v:mkAbsDir says that

due to the nature of absolute paths this (e.g. /home/foo) may compile on your platform, but it may not compile on another platform (Windows).

Steps to Reproduce

Run stack build on the repo on Windows system.

Expected Result

Compilation suceeds.

Actual Result

Compilation fails:

�[0mluna-package-0.2: build (lib)�[0m
Progress 1/2

--  While building custom Setup.hs for package luna-package-0.2 using:
      C:\sr\setup-exe-cache\x86_64-windows\Cabal-simple_Z6RU0evB_2.2.0.1_ghc-8.4.2.exe --builddir=.stack-work\dist\7d103d30 build lib:luna-package --ghc-options " -ddump-hi -ddump-to-file -fdiagnostics-color=always"
    Process exited with code: ExitFailure 1
    Logs have been written to: F:\dev\luna\.stack-work\logs\luna-package-0.2.log

    Preprocessing library for luna-package-0.2..
    Building library for luna-package-0.2..
    [ 7 of 11] Compiling Luna.Package     ( src\Luna\Package.hs, .stack-work\dist\7d103d30\build\Luna\Package.o )

    �[;1msrc\Luna\Package.hs:278:32: �[;1m�[31merror:�[0m�[0m�[;1m�[0m�[0m�[;1m
        ? Exception when trying to run compile-time code:
            InvalidAbsDir "/"
    CallStack (from HasCallStack):
      error, called at src\\Path.hs:536:17 in path-0.6.1-1tx1iSEHmt775kax6VnlPP:Path
          Code: Path.mkAbsDir "/"
        ? In the untyped splice: $(Path.mkAbsDir "/")�[0m�[0m
    �[;1m�[34m    |�[0m�[0m
    �[;1m�[34m278 |�[0m�[0m     srcPackageRoot <- fromJust �[;1m�[31m$(Path.mkAbsDir "/")�[0m�[0m <$> findPackageRoot src
    �[;1m�[34m    |�[0m�[0m�[;1m�[31m                                ^^^^^^^^^^^^^^^^^^^^�[0m�[0m
    �[0m�[0m�[0m

Luna Version

n/a

[iamrecursion]

See #277.