configure.ac: Enable option subdir-objects for automake

It silences an automake warning and keep the rootdir cleaner.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

configure.ac

@@ -4,7 +4,8 @@ AC_CONFIG_HEADER([config.h])
 AC_CONFIG_MACRO_DIR([m4])
 AC_CONFIG_AUX_DIR([build-aux])
 
-AM_INIT_AUTOMAKE([1.13 -Wno-portability foreign no-define tar-ustar no-dist-gzip dist-xz color-tests parallel-tests])
+AM_INIT_AUTOMAKE([1.13 -Wno-portability foreign no-define tar-ustar no-dist-gzip dist-xz
+                  color-tests parallel-tests subdir-objects])
 AM_MAINTAINER_MODE([enable])
 AM_SILENT_RULES([yes])
 AC_USE_SYSTEM_EXTENSIONS