[CMake] Simple CMake project on Msys2/Win10-64 gives Complex "Platform" error

[Michael Enright]

I'm getting a message that says my platform is not known to CMake,
which seems very unlikely. Here are the details.

Today, I have installed cmake using pacman on Msys2,
I created a basic CMakeLists.txt to compile a single c++ file into a
test application, called 'test'. I have tested that the source code
compiles using g++ directly.

When I try to use "cmake ." to configure this project to build, I get
a bunch of normal messages, interspersed with REPEATED output of this:
System is unknown to cmake, create:
Platform/MINGW64_NT-10.0 to use this system, please send your config
file to cmake at www.cmake.org so it can be added to cmake
-- Detecting CXX compile features - done

How do I make this message go away? A detailed walk through of how to
actually author the file mentioned is an acceptable answer.

Also, what's with the scary message about the name 'test' being reserved?

Finally, I know better, normally, than to use "cmake ." but I'm sure
that is not the source of this issue. As soon as I fix this issue I'll
throw this directory away and go back to real work.

$ cmake --version
cmake version 3.2.3
-------------- next part --------------
project(test)

    set (CMAKE_CXX_STANDARD 11)
    set (CMAKE_C_STANDARD 11)

add_executable(test test.cpp)