[Patch, Fortran] PR40276/PR57711 - improve generic diagnostic

[Dominique Dhumieres]

Dear Tobias,

After this patch several tests related to pr20896 are now rejected,
it is probably right to issue an error for them, but I am not sure
that the message is right, e.g.

! { dg-do compile }
! Test the fix for PR20896 in which the ambiguous use
! of p was not detected.
!
! Contributed by Joost VandeVondele <jv244@cam.ac.uk>
!
  INTERFACE g
    SUBROUTINE s1(p) ! { dg-error "is already being used" }
      INTERFACE
        SUBROUTINE p
        END
      END INTERFACE
    END
    SUBROUTINE s2(p) ! { dg-error "Global name" }
      INTERFACE
        REAL FUNCTION p()
        END
      END INTERFACE
    END
  END INTERFACE

      INTERFACE
        REAL FUNCTION x()
        END
      END INTERFACE
      INTERFACE
        SUBROUTINE y
        END
      END INTERFACE
  call g (x)
  call g (y)
  END
  REAL FUNCTION x()
    x = 0.1
  END
  SUBROUTINE y()
    print *, 1.5
  END
  SUBROUTINE s1(p)
    call p()
  END
  SUBROUTINE s2(p)
    print *,  p()
  END

is rejected with

pr20896_db.f90:27.20:

        SUBROUTINE y
                    1
Error: FUNCTION attribute conflicts with SUBROUTINE attribute in 'y' at (1)
pr20896_db.f90:31.10:

  call g (y)
          1
Error: Interface mismatch in dummy procedure 'p' at (1): 'y' is not a function

Note that pr20896 is still open, so this should not delay the commit, but will
require to update pr20896.

Thanks for the patch,

Dominique