Adjust `-i` paths used by ghci to point to autogen / etc files generated by newer Cabal

[mgsloan]

I think this change was introduced in Cabal >= 2. stack ghci currently adds dist/build/autogen and similar dirs to the source search path. Cabal's per component build instead puts them in dist/build/$COMPONENT/autogen.

[gahag]

This also affects flycheck for emacs. It reports it can't find autogen modules, as stack ghci does. Downgrading the resolver from lts-10.3 to lts-9.21 seems to be a temporary solution.

[mgsloan]

@gahag I've opened a PR which fixes this - #3795

[dbaynard]

Is this supposed to fix stack ghci for libraries with internal library modules? (If not, I'll open a new issue).

Edit: #3795 does fix it spoke too soon. I'll investigate further.