Auto merge of #54718 - froydnj:aarch64-ci, r=alexcrichton
add an appveyor config for aarch64-pc-windows-msvc
This is purely a cargo-cult of things to solicit feedback from humans and/or automation failures. Not sure that the build artifacts would get packaged properly to start providing nightly tarballs for `libstd`, but this is at least a start.
Fixes #53864.