If Qt5 is configured with -opengl es2 then <QtOpenGL> doesn't define
GL_PERSPECTIVE_CORRECTION_HINT.

Index: opencv-2.4.11/modules/highgui/src/window_QT.cpp
===================================================================
--- opencv-2.4.11.orig/modules/highgui/src/window_QT.cpp
+++ opencv-2.4.11/modules/highgui/src/window_QT.cpp
@@ -3118,7 +3118,9 @@ void OpenGlViewPort::updateGl()
 
 void OpenGlViewPort::initializeGL()
 {
+#ifdef GL_PERSPECTIVE_CORRECTION_HINT
     glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
+#endif
 }
 
 void OpenGlViewPort::resizeGL(int w, int h)