In any case: I use a custom Makefile (another thing I don't understand, why is CLion so obsessed with CMake? Why not let me chose my own build system?) and it's loaded properly. Using said makefile my project builds perfectly fine and runs like a charm so the error is definitely with some weird code inspections in CLion.
Here's it failing to recognize cpp imports and the std namespace
because while it knows it's a C++ project it still tries to resolve some small C file: