hg: shenandoah/jdk10: ShenandoahWriteBarrierRB flag to conditionally disable RB on WB fastpath

[ashipile at redhat.com]

Changeset: 92710862e1a5
Author:    shade
Date:      2018-01-10 13:05 +0100
URL:       http://hg.openjdk.java.net/shenandoah/jdk10/rev/92710862e1a5

ShenandoahWriteBarrierRB flag to conditionally disable RB on WB fastpath

! src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp
! src/hotspot/cpu/x86/macroAssembler_x86.cpp
! src/hotspot/share/gc/shenandoah/shenandoah_globals.hpp
! src/hotspot/share/opto/shenandoahSupport.cpp