RFR: Backport bugfixes to jdk14

[Roman Kennke]

I'd like to backport a number of (P3) bugfixes from jdk15 to jdk14:

Changesets:
http://cr.openjdk.java.net/~rkennke/backport-jdk14-2020-01-08/changesets.txt

Full webrev:
http://cr.openjdk.java.net/~rkennke/backport-jdk14-2020-01-08/webrev.00/

All changesets transplanted cleanly.

Testing: hotspot_gc_shenandoah (fastdebug/release)

Ok to go to jdk14?

Roman