RFR: 8234573: ZGC: Enable ZVerifyMarking by default in debug builds

[Per Liden]

Thanks Stefan!

/Per

On 11/21/19 12:27 PM, Stefan Karlsson wrote:
> Looks good.
> 
> StefanK
> 
> On 2019-11-21 12:11, Per Liden wrote:
>> Just like we have ZVerifyRoots enabled by default in debug builds, I 
>> think we should also enabled ZVerifyMarking, since it's fairly 
>> inexpensive.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8234573
>> Webrev: http://cr.openjdk.java.net/~pliden/8234573/webrev.0
>>
>> /Per