[Bug tree-optimization/126763] a?__builtin_clz(a):__builtin_clz(31) -> clz(a|1)

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126763

--- Comment #1 from Drea Pinski <pinskia at gcc dot gnu.org> ---
Seems like we could the a|CST trick even for this:
```
int gg(unsigned a)
{
    if (a>=3)
      return __builtin_clz(a);
    return __builtin_clz(3);
}
int gg0(unsigned a)
{
    return __builtin_clz(a|3);
}
```