[Bug sanitizer/60636] ubsan doesn't instrument signed integer ABS_EXPR

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60636

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
We should instead instrument ABS_EXPR (you can instrument that as u > 0 ? u :
-u of course).