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

[Aleksey Shipilev]

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