llvm/utils/release/download_prerequisites.bat
usage: <out_folder>
This script downloads needed dependencies in <out_folder> and create an
activate.bat script to load them on PATH.
In build_llvm_release.bat, add an option --download-prerequisites that
calls this script before doing the build.
Example: build_llvm_release.bat --version 15.0.0 --x64 --download-prerequisites
Whoa, I had not realized pushd/popd is a thing on Windows.