I did this once - and I'm not sure exactly how I did it - but basically, it's like this:
pkg-config needs to realize that this lib is installed. Do a man pkg-config, and see what it says.
You should find that .pc file somewhere in that dir (/usr/share/doc/libgnomeprint-2.4.2)
Once you have it, you have to run a command to add it to pkg-config. It's not as simple as editing a file if I remember right.
Anyway, you run the command, point it to the .pc file, and it will update the config file for you.
Do a ./configure again, and you should be good to go.