typechecker: fix trac issue #11708
typechecker: fix trac issue #11708

Summary: Fixes T11708

Reviewers: austin, bgamari, goldfire, simonpj

Reviewed By: goldfire, simonpj

Subscribers: simonpj, goldfire, thomie

Differential Revision: https://phabricator.haskell.org/D2006

GHC Trac Issues: #11708

tjakway/ghcjvm,vTurbine/ghc,snoyberg/ghc,sdiehl/ghc,ezyang/ghc,mettekou/ghc,mettekou/ghc,shlevy/ghc,shlevy/ghc,sgillespie/ghc,olsner/ghc,ezyang/ghc,tjakway/ghcjvm,sgillespie/ghc,mettekou/ghc,sdiehl/ghc,tjakway/ghcjvm,vTurbine/ghc,mettekou/ghc,olsner/ghc,sdiehl/ghc,vikraman/ghc,snoyberg/ghc,vikraman/ghc,snoyberg/ghc,shlevy/ghc,vikraman/ghc,tjakway/ghcjvm,vTurbine/ghc,sdiehl/ghc,sgillespie/ghc,snoyberg/ghc,ezyang/ghc,olsner/ghc,vikraman/ghc,sdiehl/ghc,vTurbine/ghc,olsner/ghc,mettekou/ghc,ezyang/ghc,sgillespie/ghc,tjakway/ghcjvm,snoyberg/ghc,mettekou/ghc,shlevy/ghc,tjakway/ghcjvm,tjakway/ghcjvm,shlevy/ghc,shlevy/ghc,sdiehl/ghc,shlevy/ghc,olsner/ghc,vTurbine/ghc,snoyberg/ghc,vikraman/ghc,olsner/ghc,snoyberg/ghc,sgillespie/ghc,ezyang/ghc,sgillespie/ghc,vTurbine/ghc,ezyang/ghc,mettekou/ghc,vTurbine/ghc,olsner/ghc,vikraman/ghc,vikraman/ghc,sdiehl/ghc,sgillespie/ghc,ezyang/ghc