compile error even though file was included

When I compile my C++11 on Unix I get the following error: (Even though it works fine on clion of my mac)

 /final: /lib64/libstdc++.so.6: version `GLIBCXX_3.4.21' not found (required by ./final) 

---

Update: this global variable is causing the issue but why?

std::set<std::string> testme = {"print"};