configure: build silently by default

'make V=1' will make the build verbose like before

configure.ac

@@ -39,6 +39,7 @@ AC_CONFIG_SRCDIR([lib/urldata.h])
 AC_CONFIG_HEADERS(lib/curl_config.h include/curl/curlbuild.h)
 AC_CONFIG_MACRO_DIR([m4])
 AM_MAINTAINER_MODE
+m4_ifdef([AM_SILENT_RULES], [AM_SILENT_RULES([yes])])
 
 CURL_CHECK_OPTION_DEBUG
 CURL_CHECK_OPTION_OPTIMIZE