Merge from upstream jdk/jdk12 up to tag jdk-12+26

[Roman Kennke]

As $SUBJECT says. Brings our new sh/jdk12 to latest jdk12 tag and
actually merges in Shenandoah ;-)

http://cr.openjdk.java.net/~rkennke/upstream-jdk12-merge-2019-01-09/outgoing.txt

Testing: hotspot_gc_shenandoah as usual

Ok?
Roman