I was confused on what the 'unstable' section of my .cargo/config.toml file should look like once I started getting linking errors when going through the third post. It turned out it was because I overwrote the previous 'unstable' configuration with the latter one.
In other words, I thought we were to overwrite "build-std = ["core", "compiler_builtins"]" under the "unstable" config, with "build-std-features = ["compiler-builtins-mem"]" and NOT have both present.
I think this makes it more clear that both are supposed to be present.
