Backports to sh/jdk1 2019-03-18

[Roman Kennke]

This backports recent changes from jdk12 to sh/jdk11 (it's not all that 
much, but includes the important hugeTLBFS fixes by Aleksey):

http://cr.openjdk.java.net/~rkennke/backports-jdk11-2019-03-18/changes.txt

Full webrev:
http://cr.openjdk.java.net/~rkennke/backports-jdk11-2019-03-18/webrev.00/

Backports was based for the first time on the awesomesauce backports 
monitor:
https://builds.shipilev.net/backports-monitor/label-gc-shenandoah.txt

Testing: passes hotspot_gc_shenandoah

Good to push?

Roman