Those CMake source files (e.g. CMakeCCompilerId) are used by CMake to perform some diagnostics in the process of creating build files, they really shouldn’t be getting ingested into producing that UE4Editor-ResonanceAudio.dll. UnrealBuildTool, during some step of its execution, will hunt through project subdirectories and vacuum up .cpp files when determining which objects to compile and link into libraries, and it’s doing this for the ResonanceAudio plugin. Make sure that these source files (e.g. CMakeCCompilerId.cpp) are removed before the build tool runs. I did this and it built fine. Probably these source files shouldn’t be checked in, or should be ignored as part of the build if they’re appearing because of CMake running.