Avoid Qt/X11 header contamination via egl.h

egl.h on certain platforms directly includes X11 headers, resulting in an
all too familiar header conflict. There are existing defines we merely need
to set in order to avoid this eventuality.

Change-Id: Ic91b66286ad6cc329f9c88b5e47834690a8eb96a
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>

src/plugins/platforms/eglfs/eglfs.pro

@@ -13,6 +13,9 @@ DESTDIR = $$QT.gui.plugins/platforms
 
 #DEFINES += Q_OPENKODE
 
+#Avoid X11 header collision
+DEFINES += MESA_EGL_NO_X11_HEADERS
+
 SOURCES =   main.cpp \
             qeglfsintegration.cpp \
             qeglfswindow.cpp \