The problem is most likely coming from a different version of the Ignition library which is installed in your system. In the installation instructions there is this step here
sudo apt-get install libignition-math2-dev libignition-transport-dev libignition-transport0-dev
which installs the ignition library, and it should be located in /usr/include/ignition
The specific file that CMake is complaining about should be located in /usr/include/ignition/math2/ignition/math/Vector2.hh
and should look like the file that I attach. As you can see in the file, there is a Zero function declared in line 32, which probably your version of ignition does not have. You can also see in the bitbucket of ignition that the file indeed has the zero function as a member of the vector2 class https://bitbucket.org/ignitionrobotics/ign-math/src/default/include/ignition/math/Vector2.hh. Most likely this is missing from your version. If you confirm that is the case, then you will have to remove your version of ignition and reinstall it with apt-get. Let us know if that helps.
ManosVector2.txt (13.3 KB)