Support building with cmake4

[Jakuje]

The cmake4 brings in some cutting of old versions and as it is making its way to Fedora, it fails to build. For more information, see the following Fedora Change proposal:

https://fedoraproject.org/wiki/Changes/CMake4.0

This PR adjusts the cmake_minimum_required to have higher-bound on version 4. It also rewrites the exec_program to execute_process as the former is deprecated.

I did not dig enough deep to see if the execute_process is available in cmake 2.8 (and if it does even make sense to keep support for this old cmake versions) so I can also change the supported versions to 3.5...4.0 if you do not mind, but this was the least amount of changes I had to made to make it working.