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

[Greg Marr]

> Hmmmm, well, this last point raises the question of whether the
> support you're asking is best served by the IDE developers by
> "wrapping around" CMake (or some other build tool).

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.