For many, many years `GHCForeignImportPrim` has suffered from the rather
restrictive limitation of not allowing any non-trivial types in arguments
or results. This limitation was justified by the code generator allegely
barfing in the presence of such types.

However, this restriction appears to originate well before the NCG
rewrite and the new NCG does not appear to have any trouble with such
types (see the added `T24598` test). Lift this restriction.

Fixes #24598.