RFR: Bulk integration from jdk/jdk 2018-04-23

[Roman Kennke]

This merges latest upstream changes, based on:

changeset:   50053:69d7398038c5
user:        rehn
date:        Wed Apr 18 09:25:51 2018 +0200
summary:     8195099: Concurrent safe-memory-reclamation mechanism

It brings lots of goodies, the top 3 being:

- thread local GC data (replacing our gcstate, satb queue and
oom_during_evac, possibly in the future the gclab)
- runtime object equals barriers
- interpreter/assembler GC code generator

The complete list of changes:
http://cr.openjdk.java.net/~rkennke/merge-2018-04-23/changesets

Diff of Shenandoah changes:
http://cr.openjdk.java.net/~rkennke/merge-2018-04-23/shenandoah-changes.patch

Complete webrev (give it some time to upload):
http://cr.openjdk.java.net/~rkennke/merge-2018-04-23/webrev.00

Tested: fastdebug build/PCH/non-PCH, run hotspot_gc_shenandoah,
specjvm/+VerifyStrictOopOperations

The changes from "RFR: Remove ShenandoahMarkCompactBarrierSet" are
contained here, but not in the same form as I'm going to push
separately. I'll sort it out before pushing the whole thing.

Also missing is the aarch64 port of the interpreter changes. I intend to
sort it out tomorrow.

Roman