Minimal VM did not build after integration of JDK-8199712

Minimal VM excludes INCLUDE_JFR, and the stubs complained about not having the proper declarations (Klass*, Method*, ModuleEntry*).

In closed these were statically forward declared, these declarations were lost in the new metadata system.

We should solve it by having the metadata generation layout the proper fwd declares of the types needed (inlcluding the stub section)