SSL: fixed build with LibreSSL 2.8.0 (ticket #1605). LibreSSL 2.8.0 "added const annotations to many existing APIs from OpenSSL, making interoperability easier for downstream applications". This includes the const change in the SSL_CTX_sess_set_get_cb() callback function (see 9dd43f4ef67e), which breaks compilation. To fix this, added a condition on how we redefine OPENSSL_VERSION_NUMBER when working with LibreSSL (see 382fc7069e3a). With LibreSSL 2.8.0, we now set OPENSSL_VERSION_NUMBER to 0x1010000fL (OpenSSL 1.1.0), so the appropriate conditions in the code will use "const" as it happens with OpenSSL 1.1.0 and later versions.

scgi_param  REQUEST_METHOD     $request_method;
scgi_param  REQUEST_URI        $request_uri;
scgi_param  QUERY_STRING       $query_string;
scgi_param  CONTENT_TYPE       $content_type;

scgi_param  DOCUMENT_URI       $document_uri;
scgi_param  DOCUMENT_ROOT      $document_root;
scgi_param  SCGI               1;
scgi_param  SERVER_PROTOCOL    $server_protocol;
scgi_param  REQUEST_SCHEME     $scheme;
scgi_param  HTTPS              $https if_not_empty;

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