Fix compilation of the gstreamer backend when the X11 includes are not found at /usr/include/X11
Fix compilation of the gstreamer backend when the X11 includes are not
found at /usr/include/X11

Patch by contributor KSU

KDE/phonon-gstreamer,KDE/phonon-mmf,KDE/phonon-gstreamer,shadeslayer/phonon-gstreamer,KDE/phonon-xine,shadeslayer/phonon-gstreamer,shadeslayer/phonon-gstreamer,KDE/phonon-xine,KDE/phonon-quicktime,KDE/phonon-waveout,KDE/phonon-directshow,KDE/phonon-xine,KDE/phonon-directshow