I too am experiencing the same build error mentioned at http://marc.info/?l=openbsd-ports&m=132201147610603 (I wasn't subscribed to ports@ on November 23, or I'd have replied to the original). This is on 5.0-stable on amd64; I'm guessing that it was the fix for CVE-2011-4128 in revision 1.39.2.1 of the Makefile that did it (I say that because looking at http://www.openbsd.org/cgi-bin/cvsweb/ports/security/gnutls/?only_with_tag=OPENBSD_5_0 the Makefile seems to be the only thing changed recently).
I'm no programmer, but I'd be glad to test any patches.
