message: ranges::convert_to only requires explicit convertibility, fixes
diff: @@ -137,8 +137,7 @@ namespace ranges
  template<typename T>
  struct convert_to
  {
  - template<typename U,
  - CONCEPT_REQUIRES_(std::is_constructible<T, U>::value)>
  + template<typename U>
  constexpr auto operator()(U && u) const
  RANGES_DECLTYPE_AUTO_RETURN_NOEXCEPT
  (
  