Unconditional compilation of the postpone filter. Postpone filter is an essential part of subrequest functionality. In absence of it a subrequest response body is sent to the client out of order with respect to the main request header and body, as well as other subrequests. For in-memory subrequests the response is also sent to the client instead of being stored in memory. Currently the postpone filter is automatically enabled if one of the following standard modules which are known to create subrequests is enabled: ssi, slice, addition. However a third-party module that creates subrequests can still be built without the postpone filter or be dynamically loaded in nginx built without it.