[CMake] on cmake supporting one arch per project (from CMake IR)

[Greg Marr]

"Since CMake is the one generating the project files, it is obvious that it should be the one that is updated to add this support.  The current lack of support is not due to any kind of limitation in any of the IDEs, it is purely a limitation of the tool that is generating the project files that already contain all the necessary support for the requested features, and have done so for many years now, since before the last time that the Visual Studio generators had to be rewritten to move from vcproj to vcxproj.  The generated project files can already contain multiple configurations (release vs debug), but not multiple platforms."


Gilles Khouzam from Microsoft has created an experimental fork, current as of 3.2.1, that adds this support.
https://github.com/Microsoft/CMake/tree/feature/MSMultiPlatform

Adding experimental MultiPlatform support to CMake for Windows and VS 2012 and above.

By setting the CMAKE_VS_EFFECTIVE_PLATFORMS variable, the user is able to
specify that multiple platforms should be produced for the same project.

The supported platforms are Win32, ARM and x64 (not applicable to Windows Phone)
and should be specified as a delimited string Win32;ARM;x64 for example.