[Bug libstdc++/119246] Result basic_format_arg::check_dynamic_spec is incorrect for extended floating point types

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119246

--- Comment #2 from Tomasz Kamiński <tkaminsk at gcc dot gnu.org> ---
We should also see if we can format `_Float128` and `__float128` by casting to
either of them. Similary how we handle `_Float32` and other type now.