Enum: Ensure that operations on Word fuse
Enum: Ensure that operations on Word fuse

Test Plan: Validate, verify fusion

Reviewers: austin, hvr

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2376

GHC Trac Issues: #12354

vTurbine/ghc,shlevy/ghc,sdiehl/ghc,shlevy/ghc,vTurbine/ghc,sdiehl/ghc,sgillespie/ghc,ezyang/ghc,vTurbine/ghc,ezyang/ghc,shlevy/ghc,ezyang/ghc,shlevy/ghc,ezyang/ghc,olsner/ghc,olsner/ghc,sgillespie/ghc,snoyberg/ghc,snoyberg/ghc,snoyberg/ghc,snoyberg/ghc,vTurbine/ghc,vTurbine/ghc,vTurbine/ghc,olsner/ghc,shlevy/ghc,shlevy/ghc,ezyang/ghc,olsner/ghc,mettekou/ghc,sdiehl/ghc,olsner/ghc,olsner/ghc,sgillespie/ghc,sgillespie/ghc,sdiehl/ghc,mettekou/ghc,mettekou/ghc,sgillespie/ghc,shlevy/ghc,olsner/ghc,sdiehl/ghc,sgillespie/ghc,mettekou/ghc,ezyang/ghc,mettekou/ghc,ezyang/ghc,snoyberg/ghc,mettekou/ghc,snoyberg/ghc,sdiehl/ghc,vTurbine/ghc,sgillespie/ghc,mettekou/ghc,sdiehl/ghc,snoyberg/ghc