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='2023-01-05 14:21:19 +0100'>2023-01-05</span></td><td><a href='/guix/commit/gnu/home/services?id=2127e56bd8b3ee8ae5b6cde1b7ed5bf50cf7127b'>system, home: Factorize default '.bashrc'.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
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<tr><td><span title='2022-12-01 18:56:23 +0400'>2022-12-01</span></td><td><a href='/guix/commit/gnu/home/services?id=7dddf0cc54b02dfa37884bee49a20eb88a420cba'>home: xdg: Export xdg-base/user-directories getters.</a><span class='msg-avail'>...</span></td><td>Andrew Tropin</td></tr>
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<tr><td><span title='2022-11-17 06:49:51 -0500'>2022-11-17</span></td><td><a href='/guix/commit/gnu/home/services?id=238248aac98daa8d455fc0c2244ba3e0175cb8b7'>Fix problems initially introduced in commit 543d971ed2, now reinstated.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2022-11-17 06:49:51 -0500'>2022-11-17</span></td><td><a href='/guix/commit/gnu/home/services?id=44554e7133aa60e1b453436be1e80394189cabd9'>Revert "services: configuration: Revert to a working ‘guix home’."</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2022-11-13 01:00:00 +0100'>2022-11-13</span></td><td><a href='/guix/commit/gnu/home/services?id=39e4e00f75be8055300cb0afffb8bd4b4d35f2cc'>services: configuration: Revert to a working ‘guix home’.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
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<tr><td><span title='2022-10-13 09:05:46 +0400'>2022-10-13</span></td><td><a href='/guix/commit/gnu/home/services?id=4ab434958b8e97c73e8900ebb48721de11fa3c81'>gnu: home: Add home-dbus-service-type.</a><span class='msg-avail'>...</span></td><td>( via Guix-patches via</td></tr>