I forgot to mention that I didn't have VC++ installed at all (because it's not free from all points of view).
If I remember correctly I tried installing the MinGW based Rust toolchain too, but I'll try again with the instructions you've given me.
Finding where & how to use an installed VS instance (or selecting one) in automated tooling is solved by the criminally unknown, MIT licensed, MS supported, redistributable, vswhere tool: https://github.com/microsoft/vswhere
If you're so inclined to revisit this using mingw with rust you can see how here https://rust-lang.github.io/rustup/installation/windows.html
This is far easier to automate imo