hg: shenandoah/jdk: Cherry-pick 8231250: Shenandoah: Traversal GC should keep alive weak load from heap

[zgu at redhat.com]

Changeset: 4c83ed00c058
Author:    zgu
Date:      2019-09-23 14:39 -0400
URL:       https://hg.openjdk.java.net/shenandoah/jdk/rev/4c83ed00c058

Cherry-pick 8231250: Shenandoah: Traversal GC should keep alive weak load from heap
Reviewed-by: rkennke

! src/hotspot/cpu/x86/gc/shenandoah/shenandoahBarrierSetAssembler_x86.cpp