Refactor checkHiBootIface so that TcGblEnv is not necessary.

Summary:
This patch is a prelude to implementation of hi-to-hi compatibility
checking.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>

Test Plan: validate

Reviewers: simonpj, austin

Subscribers: simonmar, relrod, carter

Differential Revision: https://phabricator.haskell.org/D35
Update Haddock submodule with Iavor's validate fix.

Signed-off-by: Edward Z. Yang <ezyang@cs.stanford.edu>