Fix FOREIGN-STRUCT-SLOT-SET-FORM for aggregate slots
Fix FOREIGN-STRUCT-SLOT-SET-FORM for aggregate slots

Avoid expanding into a form with a literal AGGREGATE-STRUCT-SLOT object.

stassats/cffi,cffi/cffi,mcna/cffi,attila-lendvai/cffi,stassats/cffi,3b/cffi,dkochmanski/cffi,mcna/cffi,cffi/cffi,stassats/cffi,cffi/cffi,3b/cffi,3b/cffi,attila-lendvai/cffi,dkochmanski/cffi,dkochmanski/cffi