libr supplies an __obj_forward definition that links to a builtin, but
as it is the only def in its object file, it is readily replaceable by
an alternative Ruamoko implementation.
The builtin version currently simply errors out (rather facetiously),
but only as a stub to allow progs to load.
Going by "standard" Objective-C, retainCount really doesn't belong in
Object itself. The way GNUStep does it is to stash retainCount in memory
just below the object by allocating extra bytes for the count and returning
a pointer just beyond those extra bytes. Now Ruamoko does the same. This
fixes the inconsistencies in structure layouts for Protocol and class
structs between qfcc generated (internal) structs and user visible structs.
