Mark BROKEN, it hasn't built in quite a while.

As explained in the comment I added:

o The port does not include graphviz's include directory, assuming it is

always in the compiler's default path (ie. /usr/include).

o The port includes <graphviz/foo.h>, while code is expected to include

<foo.h> instead, and pass -I${LOCALBASE}/graphviz instead of just
-I${LOCALBASE} to the compiler.

o The code in the development repository does a better job at fixing the

problems above, but it still relies on the deprecated libgraph library
that graphics/graphviz in ports does not install anymore.