GCC raises issues with `-Werror=non-template-friend`

subprojects/wg21_p2300_std_execution/include/execution.hpp の969-986行目から始め、GCC と -Werror=non-template-friend を使って Meson のビルドを再現してください。報告された friend 宣言を確認し、この警告をエラーとして扱った場合でもプロジェクトが引き続き正常にビルドできることを検証してください。

By default, repositories compiled using the meson build enable -Werror=non-template-friend and this causes the following errors:

../subprojects/wg21_p2300_std_execution/include/execution.hpp:969:66: error: friend declaration ‘void std::execution::__connect::tag_invoke(_Tag, std::execution::__connect::__completion<_Tag(_Args ...)>&&, _Args&& ...)’ declares a non-template function [-Werror=non-template-friend]
  969 |         friend void tag_invoke(_Tag, __completion&&, _Args&&...) noexcept;
      |                                                                  ^~~~~~~~
../subprojects/wg21_p2300_std_execution/include/execution.hpp:969:66: note: (if this is not what you intended, make sure the function template has already been declared and add ‘<>’ after the function name here)
../subprojects/wg21_p2300_std_execution/include/execution.hpp:978:76: error: friend declaration ‘std::execution::__connect::__debug_env_t<_Env> std::execution::__connect::tag_invoke(std::execution::__env::get_env_t, std::execution::__connect::__debug_receiver<_Env, std::execution::completion_signatures<_Sigs ...> >)’ declares a non-template function [-Werror=non-template-friend]
  978 |         friend __debug_env_t<_Env> tag_invoke(get_env_t, __debug_receiver) noexcept;
      |                                                                            ^~~~~~~~
../subprojects/wg21_p2300_std_execution/include/execution.hpp:985:71: error: friend declaration ‘void std::execution::__connect::tag_invoke(std::execution::__receivers::set_stopped_t, std::execution::__connect::__any_debug_receiver<_Env>&&)’ declares a non-template function [-Werror=non-template-friend]
  985 |         friend void tag_invoke(set_stopped_t, __any_debug_receiver&&) noexcept;
      |                                                                       ^~~~~~~~
../subprojects/wg21_p2300_std_execution/include/execution.hpp:986:80: error: friend declaration ‘std::execution::__connect::__debug_env_t<_Env> std::execution::__connect::tag_invoke(std::execution::__env::get_env_t, std::execution::__connect::__any_debug_receiver<_Env>)’ declares a non-template function [-Werror=non-template-friend]
  986 |         friend __debug_env_t<_Env> tag_invoke(get_env_t, __any_debug_receiver) noexcept;