swift234

The weak/unowned attributes are overloaded to mean two things:
1) on decls, they say the decl is weak/unowned.
2) in sil mode, on types, they indicate that the type has weak/unowned storage.

Since these are different things, split the SIL type attributes out to new 
attributes (sil_weak/sil_unowned) to crystalize the relationship.


Swift SVN r9270