[Bug libstdc++/109606] Unguarded `__is_same` builtin usage

[akaraevz at mail dot ru via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109606

--- Comment #4 from Alexander <akaraevz at mail dot ru> ---
^ I meant `__is_same`, not `__same_as` (typo)