cairo build problem on OS X ('ft2build.h' file not found)

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

Building graphics/cairo from 2012Q1 fails (at least using clang) with

  CC     cairo-type1-subset.lo
In file included from cairo-type1-subset.c:55:
In file included from ./cairo-ft-private.h:40:
./cairo-ft.h:46:10: fatal error: 'ft2build.h' file not found
#include <ft2build.h>
         ^
1 error generated.

I do have graphics/freetype2 installed.
I do have /usr/pkg/include/ft2build.h.
I also have /usr/X11R6/include/ft2build.h.