Pass-thru `--info` and similar to support new "cabal repl" facility

This allows `ghci-ng` to be used in via the new "cabal repl" feature
(see haskell/cabal#1404) as in

  cabal repl --with-ghc=ghci-ng"

This workaround is needed as "cabal repl" calls "ghc --info" for
detecting properties of the installed GHC.