Warn on missing home modules

Authored by Yuras on Jan 20 2017, 3:53 PM.

Description

Warn on missing home modules

Introduce a warning, -Wmissing-home-modules, to warn about home modules,
not listed in command line.

It is usefull for cabal when user fails to list a module in
exposed-modules and other-modules.

Test Plan: make TEST=MissingMod

Reviewers: mpickering, austin, bgamari

Reviewed By: bgamari

Subscribers: simonpj, mpickering, thomie

Differential Revision: https://phabricator.haskell.org/D2977

GHC Trac Issues: Trac #13129