Setup Clion on Mac after removing Xcode

So far with helps from friends, I have managed to compile source codes written in C++ and test basic stuffs using the IDE.

Following is what is in my CMakeLists.txt every time I create a new project using C++ Executables.

cmake_minimum_required(VERSION 3.8)
project(untitled)

set(CMAKE_CXX_STANDARD 11)

set(SOURCE_FILES main.cpp)
add_executable(untitled ${SOURCE_FILES})

So the issue I have is with the project I used to work on before I removed Xcode manually. 

As seen, I still have Command Line Tools.

So when I created a new project, I experienced no issue in compiling what I wanted. And the auto-generated CMakeLists.txt file contained the same content as with any previous project.

Below is the specific error message I received, and which I want to ask your advise on:

I really want to understand the issues and troubleshoot on my own in the future.

Any input will be appreciated. Thanks in advance!