[Bug fortran/54572] Use libbacktrace library

[hp at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54572

--- Comment #3 from Hans-Peter Nilsson <hp at gcc dot gnu.org> 2012-09-16 
23:16:02 UTC ---
(In reply to comment #2)
> (In reply to comment #1)
> > You need unwind frames present for this to work,

> How is this different from the current backtracing implementation in
> libgfortran?

Right, it already has that dependence, sorry for the noise.