System is unknown to cmake, create: Platform/MINGW64_NT-10.0-19044

Running from MSYS2 MinGW 64-bit with CMake 3.22.1 with gcc 11.2.0 on my fork https://github.com/SamuelMarks/fswatch/tree/multi-os-ci:

# Run from empty build dir:
cmake ..

Error:

System is unknown to cmake, create:
Platform/MINGW64_NT-10.0-19044 to use this system, please post your config file on discourse.cmake.org so it can be added to cmake

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