To build zero, we need libffi. However, the code in configure to handle libffi is not up to normal library handling standards, so it is not possible to set it using configure arguments.

When trying to rectify this, I finally got tired of the mess that libraries.m4 is. I have split it into parts, where each prominent library gets it's own file, and I've switched the logic on dependencies to be positive (i.e. linux needs alsa, not "macosx does NOT need alsa").