blocks:

• SR-258 Resilient class layout

Issue Description:

Right now, this type of thing won't link:

public class A {
internal func foo() {}
}

// In some other module:
class B : A {}

This is because the vtable for B references A.foo, which is internal. The correct solution is to fix up the vtable in the same manner that we will do for library evolution purposes. Since we can't "know" the address of A.foo, we have to let the runtime build B's vtable.