Compile stack projects without .cabal file

[VichoReyes]

haskell-compile doesn't currently detect projects unless it finds a .cabal file, so it doesn't work with projects using hpack. It would be cool if it ran stack build in those cases. An easy way to check whether something is in a stack project is by running stack path --project-root but I don't think I know enough elisp to implement it.

Note: Issue #1527 is similar, but it seems to me they're going for a more general solution. I just want an automatic "stack build".