Upgrading the windows LLVM binaries

1. download the appropriate win64 exe from http://releases.llvm.org/download.html
2. obtain the installed directories (use The Unarchiver on macOS)
3. find the directory that contains bin, include, lib, libexec, share
4. make a new directory named llvm-[version] and move the directories into it
5. zip -r llvm-[version].zip llvm-[version]
6. s3put -b servo-deps-2 --prefix $(pwd) --key_prefix msvc-deps/ --grant public-read llvm-[version].zip (requires the boto pip package)
7. update this line to reflect the new version