RFR: 8209127: ZGC: Improve error message when failing to map memory for mark stacks

[Thomas Schatzl]

Hi,

On Wed, 2018-08-08 at 14:14 +0200, Per Liden wrote:
> When failing to map memory for mark stacks, we currently always fail 
> with the message "Mark stack overflow", regardless of what the error 
> actually was. We should only say that if we actually exhausted the
> mark 
> stack space.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8209127
> Webrev: http://cr.openjdk.java.net/~pliden/8209127/webrev.0
> 

  looks good.

In this and the other two changes I just reviewed, please consider
updating copyright dates before pushing. No need for another review.

Thanks,
  Thomas