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

(cherry picked from commit 0bd7c4b4240a27d4e26290741394b31b48db7671)

GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc,GaloisInc/halvm-ghc