hg: shenandoah/jdk: Cherry-pick 8231410: Shenandoah: clone barrier should use base pointer

[zgu at redhat.com]

Changeset: 829d3468be9b
Author:    shade
Date:      2019-09-25 12:21 +0200
URL:       https://hg.openjdk.java.net/shenandoah/jdk/rev/829d3468be9b

Cherry-pick 8231410: Shenandoah: clone barrier should use base pointer
Reviewed-by: rkennke

! src/hotspot/share/gc/shenandoah/c2/shenandoahBarrierSetC2.cpp
! src/hotspot/share/gc/shenandoah/shenandoahRuntime.cpp
! src/hotspot/share/gc/shenandoah/shenandoahRuntime.hpp
+ test/hotspot/jtreg/gc/shenandoah/compiler/TestClone.java