Fixes cyclic import on OS X(#9635)

Summary: Signed-off-by: Dave Laing <dave.laing.80@gmail.com>

Test Plan: Locally tested

Reviewers: thomie, austin

Reviewed By: thomie, austin

Subscribers: simonmar, ezyang, carter, thomie

Differential Revision: https://phabricator.haskell.org/D244

GHC Trac Issues: #9635