Improved maximum errno detection. Previously, systems without sys_nerr (or _sys_nerr) were handled with an assumption that errors start at 0 and continuous. This is, however, not something POSIX requires, and not true on some platforms. Notably, on Linux, where sys_nerr is no longer available for newly linked binaries starting with glibc 2.32, there are gaps in error list, which used to stop us from properly detecting maximum errno. Further, on GNU/Hurd errors start at 0x40000001. With this change, maximum errno detection is moved to the runtime code, now able to ignore gaps, and also detects the first error if needed. This fixes observed "Unknown error" messages as seen on Linux with glibc 2.32 and on GNU/Hurd.

uwsgi_param  QUERY_STRING       $query_string;
uwsgi_param  REQUEST_METHOD     $request_method;
uwsgi_param  CONTENT_TYPE       $content_type;
uwsgi_param  CONTENT_LENGTH     $content_length;

uwsgi_param  REQUEST_URI        $request_uri;
uwsgi_param  PATH_INFO          $document_uri;
uwsgi_param  DOCUMENT_ROOT      $document_root;
uwsgi_param  SERVER_PROTOCOL    $server_protocol;
uwsgi_param  REQUEST_SCHEME     $scheme;
uwsgi_param  HTTPS              $https if_not_empty;

uwsgi_param  REMOTE_ADDR        $remote_addr;
uwsgi_param  REMOTE_PORT        $remote_port;
uwsgi_param  SERVER_PORT        $server_port;
uwsgi_param  SERVER_NAME        $server_name;