This is the resolution for NB comment GB-080 17.4.1 [cstdint.syn] Sync intmax_t and uintmax_t with C2x.

With the approval of WG14 N2888 the next C standard will resolve the long-standing issue that implementations cannot support 128-bit integer types properly without ABI breaks. C++ should adopt the same fix now, rather than waiting until a future C++ standard is rebased on C2x.

[cinttypes.syn] also mentions those types, but doesn't need a change. The proposed change allows intmax_t to be an extended integer type of the same width as long long, in which case we'd still want those abs overloads.

Recommended change: Add to [cinttypes.syn] p2 "except that intmax_t is not required to be able to represent all values of extended integer types wider than long long, and uintmax_t is not required to be able to represent all values of extended integer types wider than unsigned long long."