title: How to create directory if needed?
body: <p>I'm trying to use makefile, my problem is that I have a directory, with an <code>src</code> directory and a <code>Makefile</code>. I also use a <code>tmp</code> directory what I also have to create.
  It has object files in it. And for performance, I try not to delete these when debugging.
  If I create a rule for tmp to create it, it always rebuilds all the C files.
  So how to do this?</p>