RFR: Use jint in oom-evac-handler to match older JDKs Atomic support better

[Roman Kennke]

I believe I had a reason to do it like this, but I can't remember what
it was. But it was something fairly obvious that would blow up in tests.
Very likely I was wrong. If it passes tests, it's ok for me.

Thanks, Roman


> http://cr.openjdk.java.net/~shade/shenandoah/oom-evac-jint/webrev.01/
> 
> The problem with backports is that Atomics are not really consistent between different JDK forests.
> Notably, there is no Atomic<juint> that is needed for OOMEvacHandler. This change makes the internal
> value jint.
> 
> Testing: hotspot_gc_shenandoah, building the patch with sh/jdk9
> 
> Thanks,
> -Aleksey
>