Download Submodules Quietly Using CMake. Referenced From https://cliutils.gitlab.io/modern-cmake/chapters/projects/submodule.html

CMakeLists.txt

# Initialize Git Submodules if not already done on clone
find_package(Git QUIET)
if(GIT_FOUND AND EXISTS "${PROJECT_SOURCE_DIR}/.git")
# Update submodules as needed
    option(GIT_SUBMODULE "Check submodules during build" ON)
    if(GIT_SUBMODULE)
        message(STATUS "Submodule update")
        execute_process(COMMAND ${GIT_EXECUTABLE} submodule update --init --recursive
                        WORKING_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}
                        RESULT_VARIABLE GIT_SUBMOD_RESULT)
        if(NOT GIT_SUBMOD_RESULT EQUAL "0")
            message(FATAL_ERROR "git submodule update --init failed with ${GIT_SUBMOD_RESULT}, please checkout submodules manually")
        endif()
    endif()
else()
  message(FATAL_ERROR "Git CMake Module Not Found, Please ensure that git is installed")
endif()