just touch it

touch -r does not update full timestamp, only some granuality, meaning
make(1) will still invoke the action.

this is ac coreutils-8.10-5 on tmpfs /tmp:
$ touch -r poldek.conf.xml poldek.1
$ ls -l --full poldek.conf.xml poldek.1
-rw-r--r-- 1 glen users 11K 2013-07-08 14:56:56.298562000 +0300 poldek.1
-rw-r--r-- 1 glen users 24K 2013-07-08 14:56:56.298562293 +0300 poldek.conf.xml