sdl2: X11 support depends on MMU (fork)

Fixes:

  http://autobuild.buildroot.net/results/2f7/2f738830bf98eb7284f99c11856a8694467b3daa

Signed-off-by: Guillaume GARDET <guillaume.gardet@oliseo.fr>
Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/sdl2/Config.in

@@ -21,11 +21,13 @@ comment "DirectFB video driver needs directfb"
 config BR2_PACKAGE_SDL2_X11
 	bool "X11 video driver"
 	depends on BR2_PACKAGE_XORG7
+	depends on BR2_USE_MMU # fork()
 	select BR2_PACKAGE_XLIB_LIBX11
 	select BR2_PACKAGE_XLIB_LIBXEXT
 
 comment "X11 video driver needs X.org"
 	depends on !BR2_PACKAGE_XORG7
+	depends on BR2_USE_MMU
 
 endif