[Bug tree-optimization/126705] `ctz(a*3)` should be simplified into `ctz(a)`

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126705

--- Comment #2 from Drea Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Drea Pinski from comment #1)
> This is an example of what something which is not optimized on aarch64:
> ```
> int f12(unsigned t)
> {
>     unsigned t1 = t *3;
>     if (t1)
>       return __builtin_ctz(t*3);
>     return 32;
> }
> ```

```
int f(unsigned t)
{
    t *= 3;
    if (t) // gets optimized to using the original t.
      return __builtin_ctz(t);
    return 32;
}
```