[Bug tree-optimization/97628] format truncation false positive for O1 and mtune=nocona

[msebor at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97628

--- Comment #3 from Martin Sebor <msebor at gcc dot gnu.org> ---
Yes, I did mean 'if (num < 0) __builtin_unreachable ();' but as it turns out
that doesn't help in this case.  Casting to an unsigned type does and results
in the expected range [0, 9].