FreeBSD/src 78d020d (r354634) — sys/cddl/compat/opensolaris/kern opensolaris_atomic.c, sys/cddl/compat/opensolaris/sys atomic.h
MFC r353381: emulate illumos membar_producer with atomic_thread_fence_rel
MFC r353381: emulate illumos membar_producer with atomic_thread_fence_rel