cmake: Check for OpenGL/OpenGLES before compiling GL bits in QtGStreamerUi.
cmake: Check for OpenGL/OpenGLES before compiling GL bits in QtGStreamerUi.

QtOpenGL headers require OpenGL headers, but in some distros
you can install the first without the second.

dejunk/gstreamer,GStreamer/qt-gstreamer,tswindell/qt-gstreamer,iperry/qt-gstreamer,detrout/qt-gstreamer,iperry/qt-gstreamer,detrout/qt-gstreamer,ylatuya/qt-gstreamer,freedesktop-unofficial-mirror/gstreamer__qt-gstreamer,iperry/qt-gstreamer,ylatuya/qt-gstreamer,dejunk/gstreamer,freedesktop-unofficial-mirror/gstreamer__qt-gstreamer,nasserGanjali/QtGStreamer,comicfans/libqtgstreamer,knuesel/qt-gstreamer,knuesel/qt-gstreamer,comicfans/libqtgstreamer,GStreamer/qt-gstreamer,nasserGanjali/QtGStreamer,shadeslayer/qtgstreamer,shadeslayer/qtgstreamer,comicfans/libqtgstreamer,knuesel/qt-gstreamer,GStreamer/qt-gstreamer,shadeslayer/qtgstreamer,nasserGanjali/QtGStreamer,freedesktop-unofficial-mirror/gstreamer__qt-gstreamer,detrout/qt-gstreamer,tswindell/qt-gstreamer,ylatuya/qt-gstreamer,dejunk/gstreamer,tswindell/qt-gstreamer