CMake support files and macros for native packages are provided by the cmake
package and not by the basic filesystem.

To have a better separation and less updates of the mingw{32|64}-filesystem
package when improving cmake support, it would be helpful to have a separate
mingw32-cross-cmake package that provides the relevant rpm macros.

The condition for this is that packages that use cmake use mingw32-cross-cmake
as a build dependency.

This could also be set centrally via the project configuration.