[Bug libstdc++/95561] std::is_signed_v<__int128> is false

[glisse at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=95561

--- Comment #1 from Marc Glisse <glisse at gcc dot gnu.org> ---
Are you using -std=gnu++17 or -std=c++17 ?