graphics/cairo-gobject fails to build

[Benny Siegert <bsiegert%gmail.com@localhost>]

NetBSD-6.1_RC2 on amd64, pkgsrc-current. I get:

checking for png... yes
checking whether cairo's PNG functions feature could be enabled... yes
checking for cairo's OpenGL surface backend feature...
checking for gl... no
checking GL/gl.h usability... no
checking GL/gl.h presence... no
checking for GL/gl.h... no
checking whether cairo's OpenGL surface backend feature could be
enabled... no (gl.pc nor OpenGL headers not found)
configure: error:  OpenGL surface backend feature could not be enabled
*** Error code 1

Stop.
make: stopped in /usr/pkgsrc/graphics/cairo-gobject
WARNING: *** Please consider adding c++ to USE_LANGUAGES in the
package Makefile.
*** Error code 1

Stop.

Does anyone see the same thing? I am using native X11.