How to use LLVM's IR files as sources

Hello! I need to include a few manually authored LLVM’s IR files into my CMake project. Clang supports mixing bc, ll and cpp files when compiling a binary, however, when I list the bitcode files in add_executable/add_library they seem to be ignored (I get linker errors about undefined symbols that are defined in those files and the command line output doesn’t mention them).

What is the proper way to add the IR files into build?

CMake ignores sources with unknown “languages” associated with them. LLVM IR files would be one of those. A quick search brought up this project which may be of use. I have no idea how good/useful it is first-hand.