title: Finding compiler vendor / version using qmake
body: <p>Is there any way to get the version and vendor of the compiler used by the user through qmake? What I need is to disable building some targets of my project when g++ 3.x is used and enable them when g++ 4.x is used.</p>
  
  <p><strong>Update:</strong> Most answers targeted the preprocessor. This is something that I want to avoid. I don't want a target to be build for a specific compiler version and I want this decision to be made by the build system.</p>