gnu: Restore allegro-mesa-18.2.5-and-later.patch.

Dropped in 49405aaf5c, it's still in use
by the (leaf) allegro-5.0 package.

* gnu/packages/patches/allegro-mesa-18.2.5-and-later.patch: Newish file.
* gnu/local.mk (dist_patch_DATA): Re-add it.

gnu/local.mk

@@ -662,6 +662,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/aegisub-icu59-include-unistr.patch	\
   %D%/packages/patches/aegisub-boost68.patch                    \
   %D%/packages/patches/agg-am_c_prototype.patch			\
+  %D%/packages/patches/allegro-mesa-18.2.5-and-later.patch	\
   %D%/packages/patches/amule-crypto-6.patch			\
   %D%/packages/patches/antiword-CVE-2014-8123.patch			\
   %D%/packages/patches/antlr3-3_1-fix-java8-compilation.patch	\

gnu/packages/patches/allegro-mesa-18.2.5-and-later.patch

@@ -0,0 +1,41 @@
+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