hg: jdk/jdk: 8210045: Allow using a subset of worker threads even when UseDynamicNumberOfGCThreads is not set

[per.liden at oracle.com]

Changeset: 8896112226cb
Author:    pliden
Date:      2018-08-29 08:00 +0200
URL:       http://hg.openjdk.java.net/jdk/jdk/rev/8896112226cb

8210045: Allow using a subset of worker threads even when UseDynamicNumberOfGCThreads is not set
Reviewed-by: eosterlund, kbarrett

! src/hotspot/share/gc/shared/workgroup.hpp
! src/hotspot/share/gc/z/zArguments.cpp