How to build glad as library

Dear,
in order to avoid the use of git from arrayfire/forge, I would like to build glad as library. But to my understanding it miss something

```bash
GLAD_DEPS='clang ninja-build cmake'
CC="/usr/bin/clang"
CXX="/usr/bin/clang++"
export CC
export CXX
dnf install -y ${GLAD_DEPS}
mkdir glad/build
pushd glad/build
cmake -DCMAKE_INSTALL_PREFIX=/opt/arrayfire -GNinja ..
# build
ninja
# install
ninja install
popd
```

but ninja command do nothing
```
# ninja
ninja: no work to do.
```