add_subdirectory
Working Example
```shell gt.sandbox.checkout.commit.cleanly 9251612 \ && cd cpp \ && ./build_run.sh ```Sample CMakeLists.txt with add_subdirectory that builds submodule that is pulled from github
# Min version cmake check
cmake_minimum_required(VERSION 3.0)
# Project name
project(MyMain)
# This is pointing to submodule dir, and adding this activates
# CMakeLists.txt in that dir.
add_subdirectory(external/glfw)
# Add executable target ${PROJECT_NAME} (MyMain) will be the name of the executable.
add_executable(${PROJECT_NAME} hi_world.cpp)