RFR: 8235759: Extend GCConfig::is_gc_supported to mean supported not only included in build

[Per Liden]

Looks good and trivial.

/Per

On 12/11/19 12:38 PM, Stefan Karlsson wrote:
> Hi all,
> 
> Please review this trivial patch to allow GC to say that they are 
> unsupported even though they exists in the binary.
> 
> https://cr.openjdk.java.net/~stefank/8235759/webrev.01/
> https://bugs.openjdk.java.net/browse/JDK-8235759
> 
> There's no change in behavior, but allows ZGC to specialize 
> is_gc_supported in an up-coming patch.
> 
> This patch applies on-top of:
>   8235757: Rename SupportedGC to IncludedGC
> 
> Thanks,
> StefanK