zoecarver 9f01ac3b32 [libcxx] makes iterator_traits C++20-aware
* adds `iterator_traits` specialisation that supports all expected
  member aliases except for `pointer`
* adds `iterator_traits` specialisations for iterators that meet the
  legacy iterator requirements but might lack multiple member aliases
* makes pointer `iterator_traits` specialisation require objects

Depends on D99854.

Differential Revision: https://reviews.llvm.org/D99855
2021-04-20 11:30:08 -04:00
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2021-01-28 18:02:53 +01:00