build: fool autoreconf to do a recursive reconfiguration

We just redefine AC_CONFIG_SUBDIRS to our own empty version. autoreconf
will see this during the tracing step and will automatically reconfigure
libevent and libnl as well. This may unbreak people relying on tool
trying to regen configure without using the "autogen.sh" script.

Fix #133 (with a bit of luck)

autogen.sh

@@ -62,19 +62,14 @@ EOF
 }
 
 
-SUBDIRS=""
-for dir in *; do
-    [ -d "$dir" ] || continue
-    [ -f "$dir"/configure.ac ] || [ -f "$dir"/configure.in ] || continue
-    SUBDIRS="$SUBDIRS $dir"
-done
-
 echo "autogen.sh: start libtoolize to get ltmain.sh"
 ${LIBTOOLIZE} --copy --force
 echo "autogen.sh: reconfigure with autoreconf"
-${AUTORECONF} -vif --no-recursive -I m4 . $SUBDIRS || {
+${AUTORECONF} -vif -I m4 || {
     echo "autogen.sh: autoreconf has failed ($?), let's do it manually"
-    for dir in $PWD $SUBDIRS; do
+    for dir in $PWD *; do
+        [ -d "$dir" ] || continue
+        [ -f "$dir"/configure.ac ] || [ -f "$dir"/configure.in ] || continue
 	echo "autogen.sh: configure `basename $dir`"
 	(cd "$dir" && ${ACLOCAL} -I m4 ${ACLOCAL_FLAGS})
         (cd "$dir" && check_pkg_config)

m4/config_subdirs.m4

@@ -6,6 +6,7 @@
 # to call that late enough.
 
 AC_DEFUN([lldp_CONFIG_SUBDIRS], [
+  AC_CONFIG_SUBDIRS([$1])
   ac_sub_configure_args=
   ac_prev=
   eval "set x $ac_configure_args"
@@ -96,3 +97,6 @@ AC_DEFUN([lldp_CONFIG_SUBDIRS], [
   _AS_ECHO([$ac_msg])
   cd "$ac_popdir"
 ])
+
+# Dummy AC_CONFIG_SUBDIRS for autoreconf tracing
+AC_DEFUN([AC_CONFIG_SUBDIRS], [])