message: Fix string_view.h
diff: -#include <cstddef> // to check __GLIBCXX__
  -#if __cplusplus >= 201703L || (defined(__has_include) && __has_include(<string_view>) && !defined(__GLIBCXX__))
  -#include <string_view>
  -#else
  +#pragma once
  #define STX_NAMESPACE_NAME std
  #include "string_view.hpp"
  -#endif
  