[gfortran] Fix PR 13792: Memory corruption

[Tobias Schlüter]

Tobias Schlüter wrote:
> 2004-07-15  Tobias Schlueter  <tobias.schlueter@physik.uni-muenchen.de>
> 
> 	PR fortran/13792
> 	* simplify.c (gfc_simplify_bound): Copy the bound expression.
> 

I should add that I looked briefly through simplify.c to find other such
problems, and didn't. But there might still be more, of course.

- Tobi