I had some trouble installing/building webalizer, but this is what it took to resolve it.
First, install gd and libpng from darwinports.
sudo ln -s /opt/local/lib/libgd.dylib /opt/local/lib/libgd.1.dylib
./configure --with-png-inc=/opt/local/include --with-png=/opt/local/lib --with-gdlib=/opt/local/lib --with-gd=/opt/local/include/ --enable-dns --mandir=/usr/share