I think --nothing also implies --no-pandaphysics, which is why the particle code doesn’t build. I think the mistake is that makepanda should also not try to compile the particle code when you disable pandaphysics. I’ll check in a fix.
Note that Sources.pp is part of the ppremake build system, which isn’t related to makepanda at all.
Makepanda is simpler, and is recommended unless there’s some reason you need the full control that ppremake gives you. Very few developers need ppremake.