package/qt: Avoid X11 header collision with OpenGL/EGL

package/qt: Avoid X11 header collision with OpenGL/EGL

Including X11 headers via EGL/egl.h leads to a collision of defines
between Qt and X11. To fix this qt5 added
  DEFINES += MESA_EGL_NO_X11_HEADERS
in various files:

https://github.com/qtproject/qtbase/blob/dev/src/platformsupport/eglconvenience/eglconvenience.pri#L19
https://github.com/qtproject/qtbase/blob/dev/src/plugins/platforms/minimalegl/minimalegl.pro#L10
https://github.com/qtproject/qtbase/blob/dev/src/plugins/platforms/eglfs/deviceintegration/eglfs_x11/eglfs_x11.pro#L6
[...]

This patch fixes a similar compile error in qt4:
http://autobuild.buildroot.net/results/9b0/9b0ed92984eead89d148eaa71aff6e2f1e117837/
http://autobuild.buildroot.org/results/4fd/4fd57553336d36439fab32a7221fc8639758e887/
http://autobuild.buildroot.org/results/5cb/5cb8072f8220f7203fa79936eedcc43eab53ec66/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>