Building C++ project of Osmium tool

I do not know C++, but I need to build C++ application - Osmium tool. I have not known that it is really hard to build C++ programs. What I want is just create .exe file to merge maps. That is my simple goal.

I am a little bit stuck. According to the docs:

appveyor.yml docs says:

However,I see the error:

Guys what am I doing wrong? Please, help me! Any help would be greatly appreciated.
Or maybe you know how can I get exe file? Please, share with me