title: Variables that persist across .pro files from a subdirs pro file
body: <p>Greetings,</p>
  
  <p>I've got a .pro file that looks like:</p>
  
  <pre><code>TEMPLATE = subdirs
  SUBDIRS = foo bar
  </code></pre>
  
  <p>I want to set a variable, or define, or something in my subdirs .pro file that can be read in both the foo and bar .pro files.</p>
  
  <p>I've tried to set an environment variable with:</p>
  
  <pre><code>export TEST=something
  </code></pre>
  
  <p>but that does not work, message($$(TEST)) always shows nothing (like TEST is unset).</p>