To build on Windows, we have to build glog on Windows. But, glog doesn't build on Windows, so we had to submit a patch to the project. So, to build on Windows, we download the patched version directly from the pull request that was sent to the glog repository on GitHub.
When these patches move upstream, we need to change this to point at the "real" glog release instead of the pull request.
(For details see the `CMakeLists.txt` in `3rdparty/libprocess/3rdparty`.)