TLC (Target Language Compiler) files are used to customize the code building process. They generally come in two varieties
- System/model tlc files that help in the overall model conversion process
- Block level tlc files which describe how individual blocks (typically S-Functions) get converted to C code.
But writing them is a very advanced maneuver, and describing them in a short answer difficult. You should search the doc for the term "Introduction to the Target Language Compiler" and read the links from there to get a more detailed overview.
If you're getting an error about a missing tlc file from a package that you didn't author (i.e. Arduino) then you need to go back to the authors of that package and get it. It's not something that you're going to be able to generate yourself.