[Bug libstdc++/109758] std::abs(__float128) doesn't support NaN

[jakub at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109758

--- Comment #11 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
We'd need to bitcast with
  struct
  {
#if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
    uint64_t __high;
    uint64_t __low;
#else
    uint64_t __low;
    uint64_t __high;
#endif
  } __words64;
};
and back (we can't use __uint128_t unconditionally).