[cfg] [RFC] Real datastructure for dominance information

[DJ Delorie]

> I think I am getting to the stage when I would like to install it to
> mainline tree, so does it sound sane to you if I put it into the gcc
> tree until copyright assignment is filed and we get some experience
> with ABI and try to move it to libiberty later?

I have no problem with moving a file from gcc to libiberty in the
future, if the file proves to be stable and globally useful.