RFR: couple small strip mining fixes

[Roland Westrelin]

>> Wait! Need to check if this is neutral under !UseShenandoahGC.
>
> ...or not. I suppose this is the loop strip mining code that would be replaced by the upstream LSM
> code you are doing now? If so, we can keep it in sh/jdk10. This would not be backported anyhow,
> since LSM is present only in sh/jdk10. Does this capture the intent right?

Yes, right.

Roland.