4796193cdb
* `lwsync` is a write memory barrier.
- `eieio` is really not meant for this type of operation.
* `lwsync` can also be used for the read memory barrier according to
my reading of the of the Power 8 ISA docs (v2.07)
- https://www-01.ibm.com/marketing/iwm/iwm/web/reg/download.do?source=swg-opower&S_PKG=dl&lang=en_US&cp=UTF-8
* References https://github.com/pmix/pmix/pull/391
Signed-off-by: Joshua Hursey <jhursey@us.ibm.com>