In the latest version (0.5.3+git20190105), `<X11/xlib.h>` isn't directly
included in `fb_imlib2.c` anymore, however it's used by `<Imlib.h>`
which broke our patch which disables X11 here.
Hydra build failure: https://hydra.nixos.org/build/93730733
See also 2266d1bd98