[CMake] Invoke-Build support

[Stephen Kelly]

Nagy-Egri Máté Ferenc via CMake wrote:

> I wasn’t hoping for much enthusiasm, but at least some feedback would be
> welcome. Am I making any sense here? Would such work be completely
> useless? 

On the issue of parallelism, jom builds in parallel using NMake makefiles.

Apart from that, discussion of a new generator you want to write/contribute 
belongs on the cmake-developer mailing list.

Thanks,

Steve.