Patch to allow Ada to work with tree-ssa

[Paul Brook]

> > What I meant by "easily support" is that since it's needed for Ada
> > anyway, the cost of doing it for C too is trivial.
>
> If it's only truely needed for Ada, then it could beconstrained to the
> Ada front end and have *no* impact on the rest of the compiler (but
> I've not been closely following this thread and it looks like fortran
> has some uses wrt arrays with varying strides and I guess there
> are reasons to make it visible in gimple).

Fortran needs arrays with varying size/stride. However these are always either 
pointers or automatic variables. We currently implement most automatic arrays 
via pointers and malloc/free in the frontend.

We never put variable sized objects inside aggregates.

Paul