haskell changes

[Robert Vollmert]

Hi,

I have some Haskell-related changes ready for review and ideally merge
on wip-haskell-updates.

I’ve tested them locally to the extent I managed; is CI broken or did I break
something there? http://ci.guix.gnu.org/jobset/wip-haskell-updates

Changes are:
1. move libraries out of haskell.scm (mostly into haskell-xyz.scm, those
without ghc- prefix into haskell-apps.scm), as per
https://lists.gnu.org/archive/html/guix-devel/2019-07/msg00070.html
(I’m happy to remove haskell-apps also as suggested there, would you prefer
I do that right away?)
2. apply John Soo’s patches to add hoogle (#36545)
3. apply my patch to add the elm compiler (#36665)

Cheers
Robert