title: Makefile conditional OR for definitions
body: <p>I have a Makefile with 2 ifdef conditions that perform same action when that particular config is selected.</p>
  <pre><code>     #ifdef A
       //perform C
       #endif /* A */
  
       #ifdef B
       //perform C
       #endif /* B */
  
       #ifdef A || B
       //perform C
       #endif
  </code></pre>
  <p>Last code block is not working. What is the right way to execute it in Makefile?</p>