[Bug modula2/117948] Forward procedure declaration should only be available in ISO

[gaius at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117948

--- Comment #2 from Gaius Mulley <gaius at gcc dot gnu.org> ---
Created attachment 59812
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=59812&action=edit
Proposed fix