RFR: JDK-8224836: Backout: JDK-8224626: Shenandoah: Elide barriers on uncommon traps

[Roman Kennke]

This is a clean backout of "JDK-8224626: Shenandoah: Elide barriers on
uncommon traps". This seems to cause failures in a ctw test. It seems a
bit odd that this would cause problems, but life's too short to debug
this ;-)

http://cr.openjdk.java.net/~rkennke/JDK-8224836/webrev.00/

Testing: the failing ctw test, hotspot_gc_shenandoah

Ok?

Roman