PPC: Implement SMP primitives using gcc built-ins

PPC: Implement SMP primitives using gcc built-ins

PPC: Implement SMP primitives using gcc built-ins

The SMP primitives were missing appropriate memory barriers
(sync, isync instructions) on all PowerPCs.

Use the built-ins _sync_* provided by gcc and clang. This
reduces code size significantly.

Remove broken mark for concprog001 on powerpc64. The referenced
ticket number (11259) was wrong.

Test Plan: validate on powerpc and ARM

Reviewers: erikd, austin, simonmar, bgamari, hvr

Reviewed By: bgamari, hvr

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D2225

GHC Trac Issues: #12070

(cherry picked from commit 563a4857abcee4a6e43c68323274309c58f42aa0)

Gbp-Pq: Name ppc-smp-primitives