I have a solution that contains C# and managed C++ projects.
It compiles in the solution platform x64 and x86. Since it is managed C++ I wanted to create a 'Any CPU' solution and get rid of the old ones.
I changed the C++ project linker settings to Force Safe IL Image for both x64 and x86.
Next, using the Configuration Manager, I created a new solution platform called 'Any CPU'. Next I added a project platform also called 'Any CPU'.
I proceeded to set all the C# projects to 'Any CPU', but for the C++ I can't do that. The project platform 'Any CPU' is not in the drop down, and there is also no option 'New...'.
VS is adement about it, so I kept it like it was and started a build. To my surprise the result DLL (from the C++ project) was MSIL even though the platform for C++ was x64. Same happens when compiling x32, the resulting DLL is in MSIL.
Why can't I set the C++ project to 'Any CPU'?
As far as I know, you cannot create an "AnyCPU" project type in Visual Studio for a C++/CLI project. However, you can configure your C++/CLI project (under the "Win32" project type) so that it compiles as pure, safe MSIL, without a target platform. Doing so will allow your C++/CLI DLL assembly to be used with an "AnyCPU" C# project. I.e. it's effectively "AnyCPU", even though that's not its actual name in the Configuration Manager.
In the "C/C++" project settings:
Safe MSIL Common Language RunTime Support (/clr:safe)
In the "Linker" project settings: