Patch to work around incompatibility between irrlicht-1.8.1 and mesa-10.x.
Upstream bug (fixed in trunk): http://sourceforge.net/p/irrlicht/bugs/429/
Upstream fix: http://sourceforge.net/p/irrlicht/code/4810
This patch copied from:
http://sources.gentoo.org/cgi-bin/viewvc.cgi/gentoo-x86/dev-games/irrlicht/files/irrlicht-1.8.1-mesa-10.x.patch?view=markup

From 244d00280c1b082ca164f92337773e9e4e1a3898 Mon Sep 17 00:00:00 2001
From: hiker <henrichsjoerg@mgail.com>
Date: Wed, 26 Feb 2014 11:13:03 +1100
Subject: [PATCH] Applied patch from jpirie for fixing mesa 10 compilation
 problems.

--- irrlicht-1.8.1/source/Irrlicht/COpenGLExtensionHandler.h
+++ irrlicht-1.8.1/source/Irrlicht/COpenGLExtensionHandler.h
@@ -21,6 +21,7 @@
 	#endif
 	#include <GL/gl.h>
 	#if defined(_IRR_OPENGL_USE_EXTPOINTER_)
+		typedef void (APIENTRYP PFNGLBLENDEQUATIONPROC) (GLenum mode);
 		#include "glext.h"
 	#endif
 	#include "wglext.h"
@@ -35,6 +36,7 @@
 	#endif
 	#include <OpenGL/gl.h>
 	#if defined(_IRR_OPENGL_USE_EXTPOINTER_)
+		typedef void (APIENTRYP PFNGLBLENDEQUATIONPROC) (GLenum mode);
 		#include "glext.h"
 	#end</td></tr></table>
<table class='tabs'><tr><td>
<a href='/guix/about/'>about</a><a href='/guix/'>summary</a><a href='/guix/refs/?id=d8a046d560e8e149e903b7d3648c7218bf17c085'>refs</a><a href='/guix/log/gnu/packages/graphviz.scm'>log</a><a href='/guix/tree/gnu/packages/graphviz.scm?id=d8a046d560e8e149e903b7d3648c7218bf17c085'>tree</a><a href='/guix/commit/gnu/packages/graphviz.scm?id=d8a046d560e8e149e903b7d3648c7218bf17c085'>commit</a><a class='active' href='/guix/diff/gnu/packages/graphviz.scm?id=d8a046d560e8e149e903b7d3648c7218bf17c085&amp;id2=ace3e549737e7bd935bebeb69b13087d8f0ccd6d'>diff</a></td><td class='form'><form