RFR: JDK-8202676: AArch64: Missing enter/leave around barrier leads to infinite loop

[Roman Kennke]

In aarch64's
TemplateInterpreterGenerator::generate_Reference_get_entry(void), there
used to be enter()/leave() calls around the g1 pre-barrier. This is
necessary in case the barrier calls into the runtime, to setup/remove
stack frames for the call. With the interpreter BarrierSetAssembler
work, this seems to have been dropped. It does lead to stack corruption,
sometimes endless loops, etc.

This patch re-instates the enter() and leave() calls around the barrier
where they used to be.

http://cr.openjdk.java.net/~rkennke/JDK-8202676/webrev.00/

Can I please get a review?

Thanks, Roman