RFR: Fix dangling write-barrier in acmp

[Aleksey Shipilev]

On 12/12/18 3:50 PM, Roman Kennke wrote:
> Ok, how about those?
> 
> JDK8u:
> http://cr.openjdk.java.net/~rkennke/fix-acmp-jdk8u/

UseShenandoahGC is missing here.

> JDK11:
> http://cr.openjdk.java.net/~rkennke/fixacmp-jdk11/webrev.01/

Good.

-Aleksey