title: qmake subdirs optional target/sub project
body: <p>I wondering if there is such a thing like optional targets or sub project in <em>qmake</em>, the Qt build tool.</p>
  
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  <p><strong>Project</strong></p>
  
  <p>In my test example I have a subdirs project which contains another two projects, one shared library and one basic application. The application depends on the library which works great. Additionally I have one additional compiler (invoking <em>lrelease</em>) and one additional target (invoking <em>lupdate</em>), which also works like a charm (the shared library provides them as pri file for multiple projects).</p>
  
  <p>After a complete build in release mode, the Windows deployment tool (namely <em>windeployqt.exe</em>) is called and deploys the target with all required shared libraries and plugins to my deployment directory.</p>
  
  <p>Last component I wish to add is the creation of an installer using the <strong>Qt Installer Framework</strong>, which in fact should be easily done one the executables are located. Thus I want to create another sub project which contains all the installer stuff and provides the <em>qmake</em> steps to create one. But the project should not be build all the time but only when I want to, preferably over the create menu of <em>Qt Creator</em>.</p>
  
  <p><strong>Question</strong></p>
  
  <p>Is there any way to make a <em>qmake</em> subdirs sub project fully optional, so it will not be built using the default build all?</p>