Adds a mapping to keep track of vtable LLVM IR decls/defs for use.
Adds the vtable_id to the vtable_ptr initialize instruction for lookup.
Adds emission of vtable declarations for use outside the file that
defines the vtable. (this isn't done lazily, it's done for any imported
class - it could be done lazily & maybe eventually has to be lazy to
handle generics)
David Blaikie
8e7bb2f953