RFR(xs): 8078504: Zero fails to build.

[Severin Gehwolf]

Hi,

Could somebody please review and sponsor this trivial Zero build fix? It
concerns files in the zero directory only.

Bug: https://bugs.openjdk.java.net/browse/JDK-8078504
Webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8078504/webrev.01/

One issue was caused by JDK-8026049 since it added a
VM_Version::initialize() function which wasn't declared. The other issue
concerned a missing include file.

After this change Zero again builds for all variants: release,
fastdebug, slowdebug.

Thanks,
Severin