See here
When git cloneing e.g. AudibleInstruments, use --recurse-submodules
git clone --recurse-submodules https://github.com/VCVRack/AudibleInstruments
Make sure RACK_DIR points to the Rack SDK. Get the Rack SDK from here at vcvrack.
For the AudibleInstruments plugins, you can then just run make.