I'm writing a custom-action C# DLL that will be used from my WiX MSI installer. That DLL makes several pinvoke calls to another (unmanaged) DLL, which I need to include with my managed DLL (according to this post). I can do so by adding the unmanaged DLL to my C# project as a link from its compilation folder (from its C++ project in Visual Studio.)

The question is how do I add it depending on the bitness of the C# project and its type: x86 vs x64 and debug vs release?

For instance, when I build my custom-action C# DLL as x64, I need to include the 64-bit build of the unmanaged DLL. But when I build it as x86, I need a different version of the unmanaged DLL.