They purposely make it difficult and even removed documentation on building synergy to boost sales. You can find nightlies here: https://synergy-project.org/nightly
I believe there was additional information that they removed, but maybe its all there now. That was a complaint I had read somewhere else, so I'd take that specific one with a grain of salt. Still, I think it would be silly to ignore the fact that the developers have a monetary incentive to making the project hard to compile and distribute. Maybe I'm just biased, but their site and github gives me a distinct impression that they would pretty quickly shutdown all open source aspects of the project and completely close the source if they legally could. They are hiring a CTO and another engineer. Why does an open source project with this size of scope need so much money and employees? Its clear their number one goal is to make money now, not create a quality open source project. Combine this feeling I get with how they have treated users and potential contributors in the past, I would dissuade anyone from using them as a model open source project.
Is this the documentation you were referring to? Or, was it something else?
https://github.com/synergy/synergy/wiki/Compiling