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"
 	#endif
 #elif defined(_IRR_COMPILE_WITH_SDL_DEVICE_) && !defined(_IRR_COMPILE_WITH_X11_DEVICE_)
@@ -48,6 +50,7 @@
 	#define NO_SDL_GLEXT
 	#include <SDL/SDL_video.h>
 	#include <SDL/SDL_opengl.h>
+	typedef void (APIENTRYP PFNGLBLENDEQUATIONPROC) (GLenum mode);
 	#include "glext.h"
 #else
 	#if defined(_IRR_OPENGL_USE_EXTPOINTER_)
@@ -60,6 +63,7 @@
 	#include <GL/gl.h>
 	#include <GL/glx.h>
 	#if defined(_IRR_OPENGL_USE_EXTPOINTER_)
+	typedef void (APIENTRYP PFNGLBLENDEQUATIONPROC) (GLenum mode);
 	#include "glext.h"
 	#undef GLX_ARB_get_proc_address // avoid problems with local glxext.h
 	#include "glxext.h"
option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=0b2d33af03a7bfca0b58dcd5c8d551eb6927cf6b'>root</a>/<a href='/guix/log/gnu?id=0b2d33af03a7bfca0b58dcd5c8d551eb6927cf6b'>gnu</a>/<a href='/guix/log/gnu/packages?id=0b2d33af03a7bfca0b58dcd5c8d551eb6927cf6b'>packages</a>/<a href='/guix/log/gnu/packages/stb.scm?id=0b2d33af03a7bfca0b58dcd5c8d551eb6927cf6b'>stb.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/packages/stb.scm?id=0b2d33af03a7bfca0b58dcd5c8d551eb6927cf6b&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-12-13 17:48:25 +0100'>2021-12-13</span></td><td><a href='/guix/commit/gnu/packages/stb.scm?id=8394619baceb118df92e355377fd543bb1aa501a'>gnu: Simplify package inputs.</a><span class='msg-avail'>...<span class='msg-tooltip'>This commit was obtained by running:

  ./pre-inst-env guix style

without any additional argument.
</span></span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-11-15 00:12:12 +0100'>2020-11-15</span></td><td><a href='/guix/commit/gnu/packages/stb.scm?id=0e8df7403e0e340456b5420645a96da2cd343c99'>gnu: Update stb to b42009b3b9d4ca35bc703f5310eedc74f584be58.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/stb.scm (stb): Update to commit b42009b3b9d4ca35bc703f5310eedc74f584be58..
(stb-image): Update version number to 2.26.
(stb-image-write): Update version number to 1.15.
(stb-sprintf): Update version number to 1.09.
(stb-truetype): Update version number to 1.24.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2020-11-15 00:12:11 +0100'>2020-11-15</span></td><td><a href='/guix/commit/gnu/packages/stb.scm?id=6f5f60b2891b15036375be28ace1ca87e250d667'>gnu: Add stb-rect-pack.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/stb.scm (stb-rect-pack): New public variable.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>