title: Qt application failed to compile
body: <p>I just installed Qt5 and armed with "C++ GUI Programming with QT 4 (2nd edition)" i tried to compile a very app code goes like this:
  -test.pro : </p>
  
  <pre><code>SOURCES += \
    main.cpp
  QT+=widgets
  </code></pre>
  
  <p>and main.cpp : </p>
  
  <pre><code>#include &lt;QApplication&gt;
  #include  &lt;QLabel&gt;
  
  int main(int argc,char *argv[]){
      QApplication app(argc,argv);
      QLabel * label = new QLabel("hello world");
      label-&gt;show();
     return app.exec();
  }
  </code></pre>
  
  <p>Here are the errors : </p>
  
  <pre><code>19:45:21: Running steps for project test...
  19:45:21: Configuration unchanged, skipping qmake step.
  19:45:21: Starting: "/usr/bin/make" 
  g++ -Wl,-rpath,/opt/Qt5.2.0/5.2.0/gcc -Wl,-rpath,/opt/Qt5.2.0/5.2.0/gcc/lib -o test main.o   -L/opt/Qt5.2.0/5.2.0/gcc/lib -lQt5Widgets -lQt5Gui -lQt5Core -lGL -lpthread 
  /usr/bin/ld: cannot find -lGL
  collect2: error: ld returned 1 exit status
  make: *** [test] Error 1
  19:45:21: The process "/usr/bin/make" exited with code 2.
  Error while building/deploying project test (kit: Desktop Qt 5.2.0 GCC 32bit)
  When executing step 'Make'
  19:45:21: Elapsed time: 00:00.
  </code></pre>
  
  <p>I'm using ubuntu 13.10 x86.</p>