RFR 8211268: Disable unsupported GCs for Zero

[Aleksey Shipilev]

RFE:
 https://bugs.openjdk.java.net/browse/JDK-8211268

Webrev:
  http://cr.openjdk.java.net/~shade/8211268/webrev.01/

Not all GCs are supported by Zero, because it requires implementing the GC barriers in C++
interpreter. Now that we have jvm features that can selectively disable particular GCs, we can only
build supported GCs. This avoids surprise build failures like these:
  https://bugs.openjdk.java.net/browse/JDK-8211228

Testing: x86_64 Zero build, running GCBasher with the rest of GCs

Thanks,
-Aleksey