hg: shenandoah/jdk10: Match barrier fastpath checks better

[ashipile at redhat.com]

Changeset: 5eee46621175
Author:    shade
Date:      2018-01-09 16:05 +0100
URL:       http://hg.openjdk.java.net/shenandoah/jdk10/rev/5eee46621175

Match barrier fastpath checks better

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