[Patch, Fortran] Fix misleading error for PROCEDURE(interface) and abstract types

[Tobias Burnus]

Daniel Kraft wrote:
> when compiling this program:
>
>   type, abstract :: t
>   contains
>     procedure(foobar), deferred :: x
>   end type t
> end
>
> (I think it is legal but not yet supported by gfortran because of the
> deferred binding)
Well, it would be valid if you had an interface for foobar ;-)
> I'll regression test and write a ChangeLog before committing, of course.
OK. Though, I'm wondering whether changing the order is better:

+ gfc_error ("PROCEDURE(interface) not yet implemented at %C");

"PROCEDURE(interface) at %C not yet implemented[in gfortran]"

Tobias