message: work around std::is_function / noexcept compiler/stdlib incompatibilities
diff: @@ -309,9 +309,6 @@ namespace ranges
  #endif
  // Work around libc++'s buggy std::is_function
  - #if !defined(_LIBCPP_VERSION) || _LIBCPP_VERSION >= 3800
  - using std::is_function;
  - #else
  // Function types here:
  template<typename T>
  char (&is_function_impl_(priority_tag<0>))[1];
  @@ -333,7 +330,6 @@ namespace ranges
  struct is_function
  : meta::bool_<sizeof(detail::is_function_impl_<T>(priority_tag<3>{})) == 1>
  {};
  - #endif
  template<typename T>
  struct remove_rvalue_reference
  