The c++ implementation of Sessionless wraps the c bitcoin-core secp256k1 library. It has been tested on Mac, Linux, and Arduino. c++ doesn't really have a package manager, so you'll want to include sessionless from git. Check the CMakeLists.txt in src/cpp/client/example for instructions on how to do this.
If you somehow get here before I update c++, it's not quite up to the protocol spec yet since it uses sha256 to hash messages instead of keccak256.
The update is hanging out up on the arduino branch, and should be merged soon.