RFR: Cherry-pick: JDK-8228369 and JDK-8229470 to sh/jdk

[Roman Kennke]

I'm gonna need the two for C1 SFX impl:

changeset:   56916:73d07373584c
user:        rkennke
date:        Mon Aug 12 23:37:48 2019 +0200
summary:     Cherry-pick: 8228369: Shenandoah: Refactor LRB C1 stubs

changeset:   56917:8c3f4fa2c77f
tag:         tip
user:        rkennke
date:        Tue Aug 13 16:05:58 2019 +0200
summary:     Cherry-pick: 8229470: Shenandoah: Fix C1 getAndSetObject()
failure

Testing: hotspot_gc_shenandoah

Ok?

Roman