[Bug c/65881] New: no documentation of __uint128_t

[shawn at churchofgit dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65881

            Bug ID: 65881
           Summary: no documentation of __uint128_t
           Product: gcc
           Version: unknown
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: shawn at churchofgit dot com

gcc on x86_64 recognizes __uint128_t, but this is not documented along with
__int128, also there is no warning when a target does not support __uint128_t,
like there is with __int128:

triangle64.c:32:1: error: ‘__int128’ is not supported for this target

A unsigned 128-bit type is needed because it has defined integer overflow.