[14] RFR 8235829: graal crashes with Zombie.java test

[coleen.phillimore at oracle.com]

Summary: Start ServiceThread before compiler threads, and run nmethod 
barriers for zgc before adding to the service thread queue, or posting 
the events on the java thread queue.

See bug for description of the problems found with the new Zombie.java test.

open webrev at http://cr.openjdk.java.net/~coleenp/2019/8235829.01/webrev
bug link https://bugs.openjdk.java.net/browse/JDK-8235829

Ran tier1 all platforms, and tier2-8 testing, as well as rerunning 
original test failure from bug 
https://bugs.openjdk.java.net/browse/JDK-8173361.

Thanks,
Coleen