I want to install `arena', and the binary I have is expecting my
libjpeg to be dynamically loadable. I have a statically linked
libjpeg.a, but no libjpeg.so. I also have the sources, and I can
compile them and build a new libjpeg.a from scratch, but I don't know
how to make a dynamically loadable libjpeg.so. What do I need to do?