title: how to add macro defines in Qt .pro file
body: <p>I am now using asio alone in my project, which is supposed to be built as a shared library used by others.</p>
  
  <p>But I got the following error: </p>
  
  <pre><code>warning Please define _WIN32_WINNT or _WIN32_WINDOWS appropriately.
  </code></pre>
  
  <p>My question is, can I add a macro definition to my <code>.pro</code> file to avoid it.</p>
  
  <p>Can someone tell me how to do it, just like add</p>
  
  <pre><code> #define PI 3.1415926
  </code></pre>
  
  <p>to the <code>.pro</code> file.</p>