configure.ac: fix test for PostProcessor, basic Auth, digest Auth for "--enable-xx=val" case
configure.ac: fix test for PostProcessor, basic Auth, digest Auth for "--enable-xx=val" case

ghaderer/libmicrohttpd,maru/libmicrohttpd-http2,maru/libmicrohttpd-http2,ghaderer/libmicrohttpd,ghaderer/libmicrohttpd,maru/libmicrohttpd-http2