@MickPF This depends on how you are doing your development. New players often start off doing some development on their Omega2x device, eventually, you realise this a short term solution since IoT devices are by design resource poor.
The best way to do Omega2x development is to install the build system https://github.com/OnionIoT/source then you will have access to everything you need as well as the cross compiler, so you can use your more powerful desktop/notebook device for your development and then move the completed work to your Omega via scp/ftp.
The headers and libraries you are looking for are on the Onion Github,
Also refer to the docs on how to compile on the Omega: