[aarch64-port-dev ] RFR: Merge late fix from shenandoah/jdk8

[Roman Kennke]

Hi there,

right after I brought in the big Shenandoah merge, a user reported a 
bug, which is shenandoah/jdk8 specific and which I fixed on Friday. I'd 
like to include it in the integration repo. It is this fix:

http://hg.openjdk.java.net/shenandoah/jdk8/hotspot/rev/353510f8073a

It applies and merges cleanly.

Testing: it went through our CI several times over the weekend.

Roman