add_-latomic_to_ghc-prim

add_-latomic_to_ghc-prim

commit ec9aacf3eb2975fd302609163aaef429962ecd87
Author: Moritz Angermann <moritz.angermann@gmail.com>
Date:   Thu Feb 8 16:07:07 2018 +0800

    adds -latomic to. ghc-prim

    Reviewers: bgamari, hvr

    Reviewed By: bgamari

    Subscribers: erikd, hvr, rwbarton, thomie, carter

    Differential Revision: https://phabricator.haskell.org/D4378

    iliastsi: The original patch fails to correctly detect and use C11
    atomics, so I modified it based on https://phabricator.haskell.org/D5154.

Gbp-Pq: Name add_-latomic_to_ghc-prim