RFR: fix aarch64 membar elision with shenandoah

[Roman Kennke]

Am 12.07.2018 um 15:51 schrieb Roland Westrelin:
> 
> http://cr.openjdk.java.net/~roland/shenandoah/aarch64-membars-elision/webrev.02/
> 
> This fixes membar elision on aarch64 with shenandoah. Thanks to Andrew
> Dinn for verifying the change and fixing the traversal gc case.
> 
> Roland.
> 


The patch looks good.

I verified that it builds + passes tests.

I'll check the predicates in x86. They should be equivalent.

Thanks, Roman