title: How to write multiple "_or_ (i.e. ||)" conditions in Makefile.am?
body: <p>I am looking for the way to write multipule "OR" condition in Makefile.am. 
  For example, what if only MOBILE is defined and Makefile.am is written as below.</p>
  
  <pre><code>if (MOBILE || PC_CLIENT)
      # stuff
  endif
  </code></pre>
  
  <p>Unfortunately this Makefile.am code returns compile time error.</p>
  
  <p>What is the right way to do as same?</p>