title: Adding -std=gnu++11 compiler flag to QMake
body: <p>I am compiling qt5.7 on windows with mingw32 and g++.4.9.3. 
  While executing the configure.bat, I get this error :</p>
  
  <pre><code>C:\qt-everywhere-opensource-src-5.7.0\configure.bat -prefix C:\Qt-5.7 -skip qttools -skip qtwebchannel -skip qtwebengine -skip qtcharts -skip qtdatavis3d -platform win32-g++
  </code></pre>
  
  <blockquote>
    <p>C:\qt-everywhere-opensource-src-5.7.0\qtbase/qmake/library/qmakebuiltins.cpp: In member function 'QByteArray QMakeEvaluator::getCommandOutput(const QString&amp;) const':
    C:\qt-everywhere-opensource-src-5.7.0\qtbase/qmake/library/qmakebuiltins.cpp:419:94: error: '_popen' was not declared in this scope
                                    + QLatin1String(" &amp;&amp; ") + args).toLocal8Bit().constData(), "r")) {</p>
  </blockquote>
  
  <p>The command that leads to this error is :</p>
  
  <blockquote>
    <p>g++ -c -o qmakebuiltins.o -std=c++11 -DUNICODE -ffunction-sections -g  -IC:\qt-everywhere-opensource-src-5.7.0\qtbase/qmake + lot of stuff</p>
  </blockquote>
  
  <p>Also, the following code :</p>
  
  <pre><code>    #include &lt;stdio.h&gt;
  
  int main( int argc, char ** argv )
  {
       FILE * f = popen( argv[ 1 ], "r" );
       return 0;
  }
  </code></pre>
  
  <p>doesn't compile with </p>
  
  <blockquote>
    <p>g++ -std=c++11 mytest.cpp -o mytest</p>
  </blockquote>
  
  <p>but with :</p>
  
  <pre><code>&gt;g++ -std=gnu++11 mytest.cpp -o mytest
  </code></pre>
  
  <p>So the question is how can I modify the option c++11 to gnu++11 which is passed to g++ by the configure file ?
  Thank you</p>