message: third_party/fmt: Use char8_t
diff: @@ -356,7 +356,11 @@ using string_view = basic_string_view<char>;
  using wstring_view = basic_string_view<wchar_t>;
  // A UTF-8 code unit type.
  +#if FMT_HAS_FEATURE(__cpp_char8_t)
  +typedef char8_t fmt_char8_t;
  +#else
  typedef unsigned char fmt_char8_t;
  +#endif
  /** Specifies if ``T`` is a character type. Can be specialized by users. */
  template <typename T> struct is_char : std::false_type {};
  