Introduce new typedefs: const_tree, const_rtx, etc.

[Ian Lance Taylor]

Mark Mitchell <mark@codesourcery.com> writes:

> This kind of change is so massive across the source base that it will
> disrupt almost all work currently being done on branches.  Therefore, I
> will pre-approve this change and the follow-on patches to use the types
> for stage *2*.  However, even at this point, please make sure that we
> have flushed the outstanding branch patches for the next release before
> applying.  I agree that this change is an improvement, but it would be
> bad for a change of this nature to interfere with the contribution of
> important new technology.

I'll just chime in and say that you (Kaveh) will need to double-check
with the work being done on lto-branch, since they are fiddling with
internal tree structures.

In general I think this is a great idea.  (It would be even nicer if C
had some way to do recursive const, so that a recursive-const pointer
to a structure would cause all the fields in that structure in that
structure with pointer type to be themselves recursive-const.)

Ian