RFR: Upstream merge 2018-06-30

[Roman Kennke]

This merges upstream changes from jdk/jdk up to:

changeset:   51330:12133a6e2613
user:        jlahoda
date:        Fri Jun 29 10:41:10 2018 +0200
summary:     8205418: Assorted improvements to source code model


It includes some interesting (GC related) highlights:

- 8205336: Modularize allocations in assembler

- 8204540: Automatic oop closure devirtualization
 this one caused a mess and some code re-arrangements in Shenandoah, but
overall I think it's good

- 8205683: Refactor heap allocation to separate concerns
 this one caused mess and I need to work with upstream/eosterlund to
clean it up. See what I had to do in shenandoahHeap.cpp

All merged changesets:
http://cr.openjdk.java.net/~rkennke/upstream-merge-2018-06-30/outgoing.txt

Shenandoah-related diff:
http://cr.openjdk.java.net/~rkennke/upstream-merge-2018-06-30/shenandoah-changes.patch

Testing (ongoing): tier3_gc_shenandoah (fastdebug/non-PCH release/non-PCH)

As always, aarch64 *may* be broken (I gave my best). Will fix if needed
afterwards.

Roman