[tree-ssa] Make some tree-walking functions tail recursive

[Zdenek Dvorak]

Hello,

> > I keep running out of stack when compiling some huge functions (like
> > 20001226-1.c).  This patch fixes it by making walk_tree and
> > record_in_finally_tree to use tail recursion.  Bootstrapped and
> > regtested on i686.
> 
> Why doesn't your tail recursion elimination stuff eliminate them?

the first one (walk_tree), because there is no way how compiler could
know about the possibility to do tail recursion.  The second one because
I compile it without optimizations.

Zdenek