gnu: sdl: Fix incompatibility with libx11-1.6.

* gnu/packages/patches/sdl-libx11-1.6.patch: New file
* gnu-system.am (dist_patch_DATA): Add it.
* gnu/packages/sdl.scm (sdl): Add patch.

gnu-system.am

@@ -442,6 +442,7 @@ dist_patch_DATA =						\
   gnu/packages/patches/ripperx-libm.patch			\
   gnu/packages/patches/scheme48-tests.patch			\
   gnu/packages/patches/scotch-test-threading.patch		\
+  gnu/packages/patches/sdl-libx11-1.6.patch			\
   gnu/packages/patches/slim-session.patch			\
   gnu/packages/patches/slim-config.patch			\
   gnu/packages/patches/slim-sigusr1.patch			\

gnu/packages/patches/sdl-libx11-1.6.patch

@@ -0,0 +1,13 @@
+Update _XData32 declaration in SDL_x11sym.h to match that of libx11 1.6.
+
+--- SDL-1.2.15/src/video/x11/SDL_x11sym.h.~1~	2012-01-19 01:30:06.000000000 -0500
++++ SDL-1.2.15/src/video/x11/SDL_x11sym.h	2014-12-26 00:22:36.445067694 -0500
+@@ -165,7 +165,7 @@
+  */
+ #ifdef LONG64
+ SDL_X11_MODULE(IO_32BIT)
+-SDL_X11_SYM(int,_XData32,(Display *dpy,register long *data,unsigned len),(dpy,data,len),return)
++SDL_X11_SYM(int,_XData32,(Display *dpy,register _Xconst long *data,unsigned len),(dpy,data,len),return)
+ SDL_X11_SYM(void,_XRead32,(Display *dpy,register long *data,long len),(dpy,data,len),)
+ #endif
+ 

gnu/packages/sdl.scm

@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2013 David Thompson <dthompson2@worcester.edu>
+;;; Copyright © 2014 Mark H Weaver <mhw@netris.org>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -53,7 +54,8 @@
                              version ".tar.gz"))
              (sha256
               (base32
-               "005d993xcac8236fpvd1iawkz4wqjybkpn8dbwaliqz5jfkidlyn"))))
+               "005d993xcac8236fpvd1iawkz4wqjybkpn8dbwaliqz5jfkidlyn"))
+             (patches (list (search-patch "sdl-libx11-1.6.patch")))))
     (build-system gnu-build-system)
     (arguments
      '(;; Explicitly link against Xext because SDL tries to dlopen it and