Add some missing UseShenandoahGC checks to 8u

[Aleksey Shipilev]

On 09/21/2017 06:31 PM, Roman Kennke wrote:
> Am 21.09.2017 um 18:10 schrieb Roland Westrelin:
>> 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.

Except that during backporting, we would need to guard them. So it seems easier to guard them
straight in shenandoah/jdk10, test that guards work in shenandoah/jdk10, and backport the changes
verbatim.

Thanks,
-Aleksey