On NetBSD 1.5.1 seems to produce the following.  What can I do to fix
this?  I can't get MRTG to work because something is trying to find
libpng.1.0.so where I have only libpnbg.2.0.so installed.

Here are the diagnostics on building GD:

===> Applying NetBSD patches for gd-1.8.3
===> Building for gd-1.8.3
/usr/pkg/bin/libtool  gcc -I.  -I/usr/pkg/include/freetype
-I/usr/pkg/include -I/usr/X11R6/include -I/usr/X11R6/include/X11
-I/usr/X11R6/include -I/usr/pkg/include/freetype -I/usr/pkg/include
-I/usr/X11R6/include -I/usr/X11R6/include/X11 -I/usr/X11R6/include -O2
-DHAVE_XPM -DHAVE_JPEG -DHAVE_LIBTTF  -I/usr/pkg/include/freetype
-I/usr/pkg/include -I/usr/X11R6/include -I/usr/X11R6/include/X11
-I/usr/X11R6/include -I/usr/pkg/include/freetype -I/usr/pkg/include
-I/usr/X11R6/include -I/usr/X11R6/include/X11 -I/usr/X11R6/include -c
gd.c
libtool: compile: unable to infer tagged configuration
libtool: compile: specify a tag with `--tag'
*** Error code 1

Stop.

++L