title: C preprocessor: expand macro in a #warning
body: <p>I would like to print a macro value (expand the macro) in the #warning directive.</p>
  
  <p>For example, for the code:</p>
  
  <pre><code>#define AAA 17
  #warning AAA = ???
  </code></pre>
  
  <p>The desired compile-time output would be </p>
  
  <pre><code>warning: AAA = 17
  </code></pre>
  
  <p>What do I use for ???, or, how do I augment the code?</p>