Cleaning up types in php_stdiop_cast

The whole php_stdiop_cast is a proper mess. It defines php_socket_t fd but then it uses PHP_STDIOP_GET_FD which is defined as

#define PHP_STDIOP_GET_FD(anfd, data)	anfd = (data)->file ? fileno((data)->file) : (data)->fd

which is actually always int. I assume that there are some users (external code) that casting and assume that php_socket_t is returned but I think this is incorrect and they should not assume that and it should be fixed there using proper casting. That would leave plain wrapper operating just on fd which is what I think it should.

Then why does it need to even SOCK_ERR here if it's not for socket in the first place? I think it should be redefined just to -1 or some new macro created (e.g. PHP_FD_ERR).

Originally posted by @bukka in https://github.com/php/php-src/pull/17506#discussion_r1921536084

php_stdiop_cast と PHP_STDIOP_GET_FD の定義から始め、SOCK_ERR の呼び出し元と使用箇所を追跡します。issue にはファイルもテストも記載されていません。wrapper が一貫したファイルディスクリプタ型とエラーセンチネルを使用し、サポートされていない外部 cast の仮定に依存せず、影響を受ける互換性の期待事項が確認されていれば完了です。