main(NativeExecutableSpec) {
            binaries.all {
                cppCompiler.define 'ENABLE_GREETING'
            }
        }
    }
}
"""

        and:
        file("src/main/cpp/helloworld.cpp") << """
            #include <iostream>

            int main () {
              #ifdef ENABLE_GREETING
              std::cout << "Hello!";
              #endif
              return 0;
            }