[CMake] Multi-platform visual studio projects

[John Drescher]

> I have been successful with
>
> Src\build.32 and src\build.64 so that on svn update effects both.
>
> The problem, for my automated build flow, I was hoping to make a mix, 32/64 installer.. it’s a lot harder to do with two completely separate build trees :(

For this I just make separate installers. I use a naming convention
such that win32 / win64 is part of the name of the generated nsis
executable installer.

John