[PATCH] [libc++] Teach is_integral, is_[un]signed and make_[un]signed about __[u]int128_t

[Stephan Tolksdorf]

  IMHO, having support for __int128 in the type traits can be useful irrespective of whether __int128 is recognized as an extended integer type. libstdc++ does support __int128 too (except in strict ansi mode).

http://llvm-reviews.chandlerc.com/D2917