Add some missing UseShenandoahGC checks to 8u

[Roman Kennke]

Am 21.09.2017 um 18:10 schrieb Roland Westrelin:
>> Why not 9 and 10?
> Sure. But it seemed to me it was easier and more urgent to start with
> 8u.
Fine.
> So, for 9, do we agree that big and invasive changes like strip mining
> that require some refactoring and so would be too risky to ship anyway,
> should be removed?
This sounds reasonable to me.
> And, for 10, do we agree that there's no need to make non shenandoah
> specific changes that are expected to land upstream conditional under
> UseShenandoahGC?
Sure.

Thanks!

Roman