Peter Trommler authored Oct 19, 2016 and Ben Gamari committed Oct 19, 2016

On architectures with weak memory consistency a write barrier
is needed before the write to the pointer array.

Fixes #12469

Test Plan: rebuilt Stackage nightly twice on powerpc64le

Reviewers: hvr, rrnewton, erikd, austin, simonmar, bgamari

Reviewed By: erikd, bgamari

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2525

GHC Trac Issues: #12469