Thanks for your perseverance. I’ve never tried with MinGW (it wasn’t clear if they were keeping up enough to support C++14), so you’re going to have a bumpy ride here I’m afraid (visual studio should Just Work, btw).
The error looks to me suspiciously like G++ is trying to find a directory named after a Visual Studio warning code. The most likely explanation is that in our CMake, I’ve disabled that warning and have done so detecting Windows in general and not Visual Studio in particular, and so is feeding g++ meaningless options. I’ll have a look.