[Bug tree-optimization/115337] wrong code with _BitInt() __builtin_stdc_first_leading_one/__builtin_clzg (with -1 as second arg) at -O2

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115337

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Looks like the code in `cfn_clz::fold_range` in gimple-range-op.cc assume that
the return value for defining of 0 should only be positive.

`cfn_ctz::fold_range` has a similar issue too.

As a seperate note I notice:
```
// Implement range operator for CFN_BUILT_IN_POPCOUNT.
class cfn_popcount : public cfn_ffs

```
That seems wrong, popcount is not related to ffs (ffs is more related to
clz/ctz).