Fall back on ghc-stage2 when using Windows' GHCi driver
Fall back on ghc-stage2 when using Windows' GHCi driver

Reviewers: austin, hvr, bgamari, thomie

Reviewed By: thomie

Differential Revision: https://phabricator.haskell.org/D1721

(cherry picked from commit f01eb5410d7980567bf2731b9cded9a4894a3ef5)

GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc