title: Identifier for win64 configuration in Qmake
body: <p>Is there a "win64" identifier in Qmake project files? <a href="http://doc.trolltech.com/4.4/qmake-advanced-usage.html" rel="noreferrer">Qt Qmake advanced</a> documentation does not mention other than unix / macx / win32.</p>
  
  <p>So far I've tried using:</p>
  
  <pre><code>win32:message("using win32")
  win64:message("using win64")
  amd64:message("using amd64")
  </code></pre>
  
  <p>The result is always "using win32".</p>
  
  <p>Must I use a separate project-file for x32 and x64 projects, so they would compile against correct libraries? Is there any other way to identify between 32-bit and 64-bit environments?</p>