PATCH: Preserve ObjC type-casts in C++'s build_c_cast()

[David Ayers]

Ziemowit Laski wrote:
> This patch is analogous to one I installed in the C front-end a while
>  back, after much discussion as I recall. :-)  To recap: ObjC types
> differing only in protocol conformance (e.g., 'NSObject *' vs.
> 'NSObject <Foo> *') will appear equivalent to the C++ front-end,
> which is actually fine for most things, but not casts, since we want
> to retain the protocol information.

I'm a bit paranoid about the "which is actually fine for most things,
but not casts" as there are other cases where we want to retain protocol
information.  But I'll quietly assume that this precaution is taken
elsewhere also.  (Like a true variable declared 'NSObject <Foo> *' that
it will use/prefer the protocol's signature, right?

Cheers,
David