hg: shenandoah/jdk: 2 new changesets

[ashipile at redhat.com]

Changeset: c56a80805166
Author:    shade
Date:      2018-04-13 10:50 +0200
URL:       http://hg.openjdk.java.net/shenandoah/jdk/rev/c56a80805166

Add test to verify Shenandoah is not enabled by default, and enabled with the flag

+ test/hotspot/jtreg/gc/shenandoah/options/TestEnabled.java

Changeset: 55d8baa27230
Author:    shade
Date:      2018-04-13 10:56 +0200
URL:       http://hg.openjdk.java.net/shenandoah/jdk/rev/55d8baa27230

Fix AArch64 build failure

! src/hotspot/cpu/aarch64/gc/shenandoah/shenandoahBarrierSetAssembler_aarch64.cpp