You don't need to include the code in the interface folder. That code is used for things like Software-in-the-Loop (SIL) and Processor-in-the-Loop (PIL).
To reliably package the generated code and other dependencies for compilation elsewhere, you can use packNGo which is described in the documentation.
If you are generating code for another platform, make sure to set up the HardwareImplementation property of the configuration object to match the integer sizes and other properties of that platform. You can also choose from many pre-configured options by changing cfg.HardwareImplementation.ProdHWDeviceType and possibly cfg.HardwareImplementation.TargetHWDeviceType. Using the Coder app to change these settings may be easier than the command line or you can open the Coder configuration UI to edit cfg by running:
open cfg
in MATLAB.
