gnu: sdl2: Fix build on 32-bit architectures.

* gnu/packages/patches/sdl2-mesa-compat.patch: New file.
* gnu/local.mk (dist_patch_DATA): Adjust accordingly.
* gnu/packages/sdl.scm (sdl2)[source](patches): New field.

gnu/local.mk

@@ -1314,6 +1314,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/scotch-build-parallelism.patch		\
   %D%/packages/patches/scotch-integer-declarations.patch	\
   %D%/packages/patches/sdl-libx11-1.6.patch			\
+  %D%/packages/patches/sdl2-mesa-compat.patch			\
   %D%/packages/patches/seq24-rename-mutex.patch			\
   %D%/packages/patches/sharutils-CVE-2018-1000097.patch		\
   %D%/packages/patches/shishi-fix-libgcrypt-detection.patch	\

gnu/packages/patches/sdl2-mesa-compat.patch

@@ -0,0 +1,21 @@
+Do not include GLES header when OpenGL headers are already included.
+
+Taken from upstream:
+https://hg.libsdl.org/SDL/rev/369b01006eb2
+
+diff -r 4cbaffd0083b -r 369b01006eb2 src/video/SDL_video.c
+--- a/src/video/SDL_video.c	Fri Oct 11 06:18:24 2019 +0200
++++ b/src/video/SDL_video.c	Sat Oct 12 18:47:56 2019 +0200
+@@ -37,9 +37,9 @@
+ #include "SDL_opengl.h"
+ #endif /* SDL_VIDEO_OPENGL */
+ 
+-#if SDL_VIDEO_OPENGL_ES
++#if SDL_VIDEO_OPENGL_ES && !SDL_VIDEO_OPENGL
+ #include "SDL_opengles.h"
+-#endif /* SDL_VIDEO_OPENGL_ES */
++#endif /* SDL_VIDEO_OPENGL_ES && !SDL_VIDEO_OPENGL */
+ 
+ /* GL and GLES2 headers conflict on Linux 32 bits */
+ #if SDL_VIDEO_OPENGL_ES2 && !SDL_VIDEO_OPENGL
+

gnu/packages/sdl.scm

@@ -114,6 +114,7 @@ (define-public sdl2
              (uri
               (string-append "https://libsdl.org/release/SDL2-"
                              version ".tar.gz"))
+             (patches (search-patches "sdl2-mesa-compat.patch"))
              (sha256
               (base32
                "0mqxp6w5jhbq6y1j690g9r3gpzwjxh4czaglw8x05l7hl49nqrdl"))))