Export `warningGroups' and `warningHierarchies'
Export `warningGroups' and `warningHierarchies'

Reviewers: austin, mpickering, bgamari

Reviewed By: mpickering, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2806

ezyang/ghc,olsner/ghc,shlevy/ghc,olsner/ghc,olsner/ghc,olsner/ghc,shlevy/ghc,olsner/ghc,ezyang/ghc,sdiehl/ghc,ezyang/ghc,shlevy/ghc,sdiehl/ghc,shlevy/ghc,shlevy/ghc,olsner/ghc,sdiehl/ghc,sdiehl/ghc,ezyang/ghc,sdiehl/ghc,ezyang/ghc,ezyang/ghc,sdiehl/ghc,sdiehl/ghc,ezyang/ghc,olsner/ghc,shlevy/ghc,shlevy/ghc