https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113887
--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> --- #if 42 == ((__int128) +42wb) && -35 == ((__int128) +-35wb) #else #warning warn #endif works with both gcc and clang if __BITINT_MAXWIDTH__ >= 128. That said, for UINT128_C it would need to use __uint128_t rather than unsigned __int128, as the latter doesn't work in preprocessor expressions, as that is interpreted as ((0 0) +42wb) then.
