title: Run make in each subdirectory
body: <p>I have a directory (<code>root_dir</code>), that contains a number of sub-directories (<code>subdir1, subdir2, ...</code>).</p>
  <p>I want to run the <code>make</code> in each directory in <code>root_dir</code>, using  a Makefile placed in it.
  (Obviously supposed that each of <code>subdir...</code> has inside its own Makefile).</p>
  <p>So there are essentially two questions:</p>
  <ol>
  <li>How to get a list of directories in Makefile (automatically)?</li>
  <li>How to run <code>make</code> for each of the directories inside a make file?</li>
  </ol>
  <p>As I know in order to run <code>make</code> in a specific directory I need to do the following:</p>
  <pre><code>$(MAKE) -C subdir
  </code></pre>