Add checking m4 dir in autogen.sh

sflphone-gtk/autogen.sh

 #!/bin/sh
 
 # could be replaced with autoconf -v -f (verbose, force rebuild of ltmain, .in files, etc.)
+if [ ! -d "m4" ]; then
+	mkdir m4
+fi
+
 aclocal -I m4
 libtoolize --force
 autoheader