RFR: Upstream merge jdk/jdk -> shenandoah/jdk 2018-08-07

[Roman Kennke]

This merges in tags jdk-12+5  and adds corresponding
shenandoah-jdk-12+5 tag. The same 'precise'
merging+tagging procedure as last time was used.

It gives us Zhengyu's pinning and Erik Ö's SATB queue abstraction (iow,
reduced upstream exposure).

List of stuff merged in:
http://cr.openjdk.java.net/~rkennke/jdk-upstream-merge-2018-08-07/outgoing.txt

Testing: tier3_gc_shenandoah

Ok?
Roman