GLAD cmake command "ExternalProject_Add"
Hi,

How can I download GLAD using cmake function "ExternalProject_Add" for this specific configuration ?

I found some CMake code on the internet but it does not specify these options:

```cmake
# Download GLFW3 locally into the binary directory
if(DOWNLOAD_GLAD)
    message(STATUS "GLAD will be downloaded and built")
    # Download and build
    ExternalProject_Add(GLAD
        URL "https://github.com/Dav1dde/glad/archive/v0.1.29.zip"
        PREFIX ${GLAD_PREFIX}
        CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=${GLAD_PREFIX} -DGLAD_INSTALL=${GLAD_INSTALL}
        UPDATE_COMMAND "")
endif(DOWNLOAD_GLAD)
```

![image](https://user-images.githubusercontent.com/18013985/183514318-9238372e-c76b-47d2-9062-bde0af6de9dd.png)
