[Patch, Fortran] PR57697 - Fix an issue with defined assignment

[Thomas Koenig]

Hi Tobias,

> As testing showed, it didn't fix the real-world code: ForTrilinos's
> ForTrilinos_ADT_3D_Burgers_6th_Pade did still fail as it has:
> 
>          *_F.DA65 = matrix_diff_x (&parm.621);
>        _F.DA66 = ax->epetra_rowmatrix.universal; // Deref of "ax"!
> 

> Build and regtested on x86-64-gnu-linux.
> OK?

The patch is OK, also for 4.8.  Please add a test case which also
checks for the ForTrilinos failure.

	Thomas