That file is not in there, here are the contents of that folder:
[hayek:X11R6/include/GL] mpinsk% ls -l
-rw-r--r-- 1 root wheel 2276 Mar 14 2007 amesa.h
-rw-r--r-- 1 root wheel 4672 Mar 14 2007 dmesa.h
-rw-r--r-- 1 root wheel 2710 Mar 14 2007 fxmesa.h
-rw-r--r-- 1 root wheel 2232 Mar 14 2007 ggimesa.h
-rw-r--r-- 1 root wheel 89660 Mar 14 2007 gl.h
-rw-r--r-- 1 root wheel 78288 Mar 14 2007 gl_mangle.h
-rw-r--r-- 1 root wheel 342501 Mar 14 2007 glext.h
-rw-r--r-- 1 root wheel 4338 Mar 14 2007 glfbdev.h
-rw-r--r-- 1 root wheel 16668 Mar 14 2007 glu.h
-rw-r--r-- 1 root wheel 3315 Mar 14 2007 glu_mangle.h
-rw-r--r-- 1 root wheel 15234 Mar 14 2007 glx.h
-rw-r--r-- 1 root wheel 3412 Mar 14 2007 glx_mangle.h
-rw-r--r-- 1 root wheel 30134 Mar 14 2007 glxext.h
-rw-r--r-- 1 root wheel 4257 Feb 14 03:03 glxint.h
-rw-r--r-- 1 root wheel 2453 Feb 14 03:03 glxmd.h
-rw-r--r-- 1 root wheel 77887 Feb 14 03:03 glxproto.h
-rw-r--r-- 1 root wheel 10613 Feb 14 03:03 glxtokens.h
drwxr-xr-x 4 root wheel 136 Apr 12 22:56 internal
-rw-r--r-- 1 root wheel 5609 Mar 14 2007 mesa_wgl.h
-rw-r--r-- 1 root wheel 3174 Mar 14 2007 mglmesa.h
-rw-r--r-- 1 root wheel 8595 Mar 14 2007 osmesa.h
-rw-r--r-- 1 root wheel 2508 Mar 14 2007 svgamesa.h
-rw-r--r-- 1 root wheel 1360 Mar 14 2007 uglglutshapes.h
-rw-r--r-- 1 root wheel 4313 Mar 14 2007 uglmesa.h
-rw-r--r-- 1 root wheel 51274 Mar 14 2007 vms_x_fix.h
-rw-r--r-- 1 root wheel 4402 Mar 14 2007 wmesa.h
-rw-r--r-- 1 root wheel 10401 Mar 14 2007 xmesa.h
-rw-r--r-- 1 root wheel 3313 Mar 14 2007 xmesa_x.h
-rw-r--r-- 1 root wheel 5401 Mar 14 2007 xmesa_xf86.h