title: How to expand macro and delete comma
body: <p>For example I want to write my own printf() alternative, but I have to perform calculations on the variable arguments:</p>
  
  <pre><code>#define log(fmt_string, ...) my_log(fmt_string, pack_args(__VA_ARGS__), __VA_ARGS__)
  </code></pre>
  
  <p>where pack_args(...) - is a macro too.
  How should I change this code to handle the only fmt_string presence scenario?</p>
  
  <pre><code>log("Some message here");
  </code></pre>