RFR (sh/jdk8): Backport 2020-02-27, batch 2

[Roman Kennke]

This is the second batch of backports already (~1 one more expected
soon). It backports the following issues from sh/jdk11:

JDK-8224525: Shenandoah: Eliminate shenandoah verifier's side-effects
JDK-8225171: Remove leftovers in shenandoahBarrierSetC1.cpp
JDK-8226586: Shenandoah: No need to pre-evacuate roots for degenerated GC
JDK-8227676: Shenandoah: More consistent naming of LRB runtime entry points
JDK-8228364: Shenandoah: Remove unused code from ShenandoahBarrierSetC1
JDK-8228369: Shenandoah: Refactor LRB C1 stubs
JDK-8229470: Shenandoah: Fix C1 getAndSetObject() failure
JDK-8229709: x86_32 build and test failures after JDK-8228369
(Shenandoah: Refactor LRB C1 stubs)
JDK-8229865: Use explicit #include debug.hpp for STATIC_ASSERT in
gc/shenandoah/shenandoahUtils.cpp

The significant change (and diverging from sh/jdk11) is JDK-8228369, it
requires some addition to c1_Runtime_$ARCH.cpp that is
difficult/impossible to put into shenandoahBarrierSetAssembler_$ARCH.cpp
because of missing GC interfaces. But it's overall contained, so should
be ok.

"JDK-8229470: Shenandoah: Fix C1 getAndSetObject() failure" is
interesting because it's wholly different from jdk11 because of the
recent (2 days ago) getAndSetObject() fix: instead of
overriding/reverting that I keep the recent fix and sneak in the aarch64
version of it (which we've forgotten about 2 days ago) :-) I hope that's
ok. It's in the spirit of the original fix I suppose.

Changesets:
http://cr.openjdk.java.net/~rkennke/backport-shjdk8-2020-02-27-2/changesets.txt
Webrev:
http://cr.openjdk.java.net/~rkennke/backport-shjdk8-2020-02-27-2/webrev.00/

Testing: hotspot_gc_shenandoah (x86_64, aarch64): somebody should
probably check x86_32 bit because I currently can't. Aarch64 shows some
failures but no regressions: I'll check those once I'm through with all
backports. They've been pre-existing before I started with the backports
queue.

Good?

Thank you,
Roman