he@netbsd.org typed:
:>Release:        NetBSD 1.6R May 4 2003
:System: NetBSD mizar.urc.uninett.no 1.6R NetBSD 1.6R (MIZAR) #0: Sun May  4 22:45:23 CEST 2003  he@mizar.urc.uninett.no:/usr/obj/sys/arch/sparc64/compile/MIZAR sparc64
:	An attempt at building rxvt results in:
:
:cc -DHAVE_CONFIG_H -I/usr/pkg/include -I/usr/X11R6/include -DHAVE_LIBXPM -O -ffixed-g4 -I/usr/pkg/include -I/usr/X11R6/include -DDEBUG_STRICT -I/usr/X11R6/include -I/usr/X11R6/include/X11 -I.. -I. -I. -c logging.c -o logging.o
:logging.c: In function `rxvt_update_lastlog':
:logging.c:375: storage size of `llx' isn't known
:*** Error code 1
:

:>How-To-Repeat:
:	Try to build rxvt 2.7.10nb3 from pkgsrc on a recently updated
:	system; watch it fail.

:>Fix:
:	Don't know, but it is related to utmpx / lastlogx detection,
:	include files, and symbols defined when include files are
:	pulled in.

Why doesn't patch-ae work?  It checks against your NetBSD version.
What's your <sys/param.h> claiming as it's __NetBSD_Version__

Regards,
Geoff