[aarch64-port-dev ] RFR: Bulk integration of Shenandoah

[Roman Kennke]

This integrates latest Shenandoah changes from shenandoah/jdk8u
repository. It's all backports from sh/jdk -> sh/jdk10 -> sh/jdk9 ->
sh/jdk8u or jdk8u specific bugfixes. It's all been reviewed, baked and
thoroughly tested upstream.

With Aleksey's proposed changes, the differences between this
integration and sh/jdk8u are only few whitespace changes.

The integration brings lots of major and minor improvements, bugfixes
and tests.

The list of changesets to be pushed is this:
http://cr.openjdk.java.net/~rkennke/jdk8u-shenandoah-integration-2018-03-22/jdk8u-shenandoah-integration-2018-03-22.txt

The complete webrev is:
http://cr.openjdk.java.net/~rkennke/jdk8u-shenandoah-integration-2018-03-22/webrev.02/

It builds release+fastdebug, and passes all hotspot_gc_shenandoah tests.

I'll tag the forest with:

aarch64-shenandoah-jdk8u162-b12--shenandoah-merge-2018-03-22

... after both Aleksey's change and this integration are pushed and merged.