w3m-nox: fix build

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 https://github.com/tats/w3m/commit/2266d1bd988daed273992e7b26fbeba030002b82

pkgs/applications/networking/browsers/w3m/no-x11.patch

@@ -1,14 +1,13 @@
 Forget about X11 in fb module.
 This breaks w3mimgdisplay under X11, but removes X11 dependency it in pure fb.
 diff --git a/w3mimg/fb/fb_imlib2.c b/w3mimg/fb/fb_imlib2.c
-index ea36637..d3d7bc3 100644
+index 1a5151c..d3d7bc3 100644
 --- a/w3mimg/fb/fb_imlib2.c
 +++ b/w3mimg/fb/fb_imlib2.c
-@@ -3,7 +3,7 @@
+@@ -3,6 +3,7 @@
                  fb_imlib2.c 0.3 Copyright (C) 2002, hito
   **************************************************************************/
  
--#include <X11/Xlib.h>
 +#define X_DISPLAY_MISSING
  #include <Imlib2.h>
  #include "fb.h"