[Bug middle-end/67662] -fsanitize=undefined cries wolf for X - 1 + X when X is 2**30

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67662

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
Yeah, r122414 fixed the PR30364 issue incompletely, leaving a special-case that
still mishandles this case.  Testing a patch.