Fixes compilation with Mesa >= 18.2.5.

Taken from upstream:

https://github.com/liballeg/allegro5/commit/a40d30e21802ecf5c9382cf34af9b01bd3781e47

diff --git a/include/allegro5/allegro_opengl.h b/include/allegro5/allegro_opengl.h
index 0f86a6768..652dd024e 100644
--- a/include/allegro5/allegro_opengl.h
+++ b/include/allegro5/allegro_opengl.h
@@ -103,10 +103,14 @@

 /* HACK: Prevent both Mesa and SGI's broken headers from screwing us */
 #define __glext_h_
+#define __gl_glext_h_
 #define __glxext_h_
+#define __glx_glxext_h_
 #include <GL/gl.h>
 #undef  __glext_h_
+#undef  __gl_glext_h_
 #undef  __glxext_h_
+#undef  __glx_glxext_h_

 #endif /* ALLEGRO_MACOSX */

diff --git a/include/allegro5/opengl/GLext/glx_ext_defs.h b/include/allegro5/opengl/GLext/glx_ext_defs.h
index 49c502091..fba8aea5d 100644
--- a/include/allegro5/opengl/GLext/glx_ext_defs.h
+++ b/include/allegro5/opengl/GLext/glx_ext_defs.h
@@ -1,7 +1,9 @@
 /* HACK: Prevent both Mesa and SGI's broken headers from screwing us */
 #define __glxext_h_
+#define __glx_glxext_h_
 #include <GL/glx.h>
 #undef __glxext_h_
+#undef __glx_glxext_h_

 #ifndef GLX_VERSION_1_3
 #define _ALLEGRO_GLX_VERSION_1_3
--
2.20.0
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<tr><td><span title='2023-03-20 18:49:06 +0100'>2023-03-20</span></td><td><a href='/guix/commit/gnu/services/dbus.scm?id=ccb62d8feb50e2859d7c41429a9e3d9e0fe30bfe'>Merge remote-tracking branch 'origin/master' into core-updates</a></td><td>Andreas Enge</td></tr>
<tr><td><span title='2023-03-03 17:55:35 +0100'>2023-03-03</span></td><td><a href='/guix/commit/gnu/services/dbus.scm?id=2799ad44234be675f018115f99be98d2c9fd565d'>services: dbus: Deprecate 'dbus-service' procedure.</a><span class='msg-avail'>...</span></td><td>Bruno Victal</td></tr>
<tr><td><span title='2023-03-03 17:55:34 +0100'>2023-03-03</span></td><td><a href='/guix/commit/gnu/services/dbus.scm?id=ffc5d42fc2589c349579c00e9dd11fabdff2663b'>services: dbus: Deprecate 'polkit-service' procedure.</a><span class='msg-avail'>...</span></td><td>Bruno Victal</td></tr>
<tr><td><span title='2023-01-30 12:39:40 +0200'>2023-01-30</span></td><td><a href='/guix/commit/gnu/services/dbus.scm?id=4cf1acc7f3033b50b0bf19e02c9f522d522d338c'>Merge remote-tracking branch 'origin/master' into core-updates</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2023-01-16 15:08:22 +0800'>2023-01-16</span></td><td><a href='/guix/commit/gnu/services/dbus.scm?id=daa471a7382cc49c1c8ecc0e57a42f1a91b28a6e'>gnu: services: Export polkit-configuration.</a><span class='msg-avail'>...</span></td><td>Zhu Zihao</td></tr>