[Bug tree-optimization/92408] strlen(s) != 0 not folded into *s

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92408

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note we might want to do this only when PROP_last_full_fold is set (or at least
to begin with).