Upstream merge to jdk-13+8

[Roman Kennke]

Merged trivially. Testing hotspot_gc_shenandoah seems fine.

Changes:
http://cr.openjdk.java.net/~rkennke/upstream-jdk13-merge-2019-02-14/changes.txt

In particular:
- 8217874: Shenandoah: Clobbered register in
ShenandoahBarrierSetAssembler::cmpxchg_oop()

 Ok to push?

Thanks,
Roman