title: How to preprocess makefiles
body: <p>How to show the makefile after it's been preprocessed? For example, if we have two makefiles:</p>
  
  <pre><code># Makefile
  include Makefile2
  
  # Makefile2
  a:a.c
      gcc -o a a.c
  </code></pre>
  
  <p>Then <code>&lt;preprocessor&gt; Makefile</code> should give:</p>
  
  <pre><code>a:a.c
      gcc -o a a.c
  </code></pre>
  
  <p>It's similar to what a C preprocessor does (<code>gcc -E</code>). Is there such a makefile preprocessor?</p>