[Bug c++/108099] ICE when parsing signed __int128_t typedef

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108099

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
__int128_t is already a typedef, so you can't add a signed or unsigned
qualifier to it.

std::make_signed_t<__int128_t> works because that doesn't just add the 'signed'
keyword to it.

The keyword for the type is __int128 not __int128_t, so you can say signed
__int128 and unsigned __int128.