Simon Jakobi authored Jul 26, 2018 and Ben Gamari committed Jul 27, 2018

We already include -haddock in the GhcLibHcOpts in order to include
the boot libraries' docs in their .hi-files.

By including -haddock in the GhcStage2HcOpts and GhcStage3HcOpts, we
make the docs for the ghc library also available to the GHCi :doc
command.

Reviewers: bgamari

Reviewed By: bgamari

Subscribers: rwbarton, thomie, carter

Differential Revision: https://phabricator.haskell.org/D4913