[Bug libstdc++/67214] undefined behaviour in std::num_get::_M_extract_int()

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67214

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Fixed on trunk, but let's keep the bug report open, as this is worth
backporting.