RFR: 8214476: ZGC: Build ZGC by default

[Per Liden]

Thanks for reviewing, Roman!

/Per

On 11/29/18 2:16 PM, Roman Kennke wrote:
> Yes! Great! Patch looks good!
> 
> Roman
> 
> 
>> At one point, it was decided that experimental VM features (such as ZGC)
>> should be not be built by default. This policy was later
>> changed/abandoned, so we should enable building of ZGC by default.
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8214476
>> Webrev: http://cr.openjdk.java.net/~pliden/8214476/webrev.0
>>
>> /Per
>