Cherry pick native barrier related changes to shenandoah/jdk

[Roman Kennke]

I just pushed my last-week's merge which includes the first two of your
cherry-picks and you may want to wait for my 8227637 cherry-pick too, so
that we can finally have an unbroken sh/jdk.

Roman


> I would like cherry pick native barrier related changes to shenandoah/jdk.
> 
> Cherry-pick: 8226823: Adjust BarrierSetC2 for C2 runtime calls
> Cherry-pick: 8226822: GC interface for C1 runtime calls
> Cherry-pick: 8226695: Shenandoah: Wire C1 and C2 IN_NATIVE barrier
> Cherry-pick: 8225483: Shenandoah: Enhance native access barrier
> 
> Webrev:
> http://cr.openjdk.java.net/~zgu/shenandoah/native_barriers/webrev.00/
> 
> Test:
>   in progress.
> 
> Thanks,
> 
> -Zhengyu