hg: shenandoah/jdk: fix aarch64 membar elision with shenandoah

[rwestrel at redhat.com]

Changeset: 1b2c7b2dd108
Author:    roland
Date:      2018-07-12 15:42 +0200
URL:       http://hg.openjdk.java.net/shenandoah/jdk/rev/1b2c7b2dd108

fix aarch64 membar elision with shenandoah

! src/hotspot/cpu/aarch64/aarch64.ad
! test/hotspot/jtreg/compiler/c2/aarch64/TestVolatiles.java
+ test/hotspot/jtreg/compiler/c2/aarch64/TestVolatilesShenandoah.java