[flang] Allow forward references to procedure interfaces in derived types...

[flang] Allow forward references to procedure interfaces in derived types (fixing flang-compiler/f18#571 more)

Original-commit: flang-compiler/f18@c1aeeae7765527c40c1934d4d4d15086bf88758f
Reviewed-on: https://github.com/flang-compiler/f18/pull/580
Tree-same-pre-rewrite: false