cmake: get rid of warnings, require cmake 3.10

[krixkrix]

I guess it is fair to require minimum cmake 3.10 everywhere?

This fixes warnings like:

CMake Deprecation Warning at Examples/MinimalSystem/CMakeLists.txt:31 (cmake_minimum_required):
  Compatibility with CMake < 3.10 will be removed from a future version of
  CMake.

  Update the VERSION argument <min> value.  Or, use the <min>...<max> syntax
  to tell CMake that the project requires at least <min> but has been updated
  to work with policies introduced by <max> or earlier.