hg: shenandoah/jdk10: Implement flag to generate write-barriers without membars.

[roman at kennke.org]

Changeset: ecb87af5e0d8
Author:    rkennke
Date:      2018-01-19 18:40 +0100
URL:       http://hg.openjdk.java.net/shenandoah/jdk10/rev/ecb87af5e0d8

Implement flag to generate write-barriers without membars.

! src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp
! src/hotspot/share/opto/compile.cpp
! src/hotspot/share/opto/shenandoahSupport.cpp