hi,
i found out that the Makefile sets the CFLAGS and LDFLAGS variables before
including bsd.prefs.mk, which is bad because they are now overriden by 
/etc/mk.conf settings (which breaks the build if CFLAGS doesn't contain the 
-I${LIBNBCOMPAT_SRCDIR} thing...)
here is a patch:

--- Makefile    2003-09-14 11:36:16.000000000 +0200
+++ Makefile.new        2003-09-14 11:34:36.000000000 +0200
@@ -32,12 +32,12 @@
 LIBNBCOMPAT_FILESDIR=  ${.CURDIR}/../../pkgtools/libnbcompat/files
 LIBNBCOMPAT_SRCDIR=    ${WRKDIR}/libnbcompat

+.include "../../mk/bsd.prefs.mk"
+
 CFLAGS+=               -I${LIBNBCOMPAT_SRCDIR}
 LDFLAGS+=              -L${LIBNBCOMPAT_SRCDIR}
 LIBS+=                 -lnbcompat

-.include "../../mk/bsd.prefs.mk"
-
 VERSION!=              ${AWK} -F '"' '/PKGTOOLS_VERSION/ {print $$2}' \
                        ${FILESDIR}/lib/version.h