The build prefix is part of the compiled compiler

[bjorn3]

This build prefix is incorrect when using rustup as rustup can install it everywhere. In addition it hurts reproducibility of builds.

rust/compiler/rustc_codegen_ssa/src/back/link.rs

Line 1581 in 3e826bb

let install_prefix = option_env!("CFG_PREFIX").expect("CFG_PREFIX");

Once this is no longer hard coded, the following line should be removed to prevent accidentally depending on it:

rust/src/bootstrap/compile.rs

Line 600 in 0148b97

.env("CFG_PREFIX", builder.config.prefix.clone().unwrap_or_default());

I noticed this as I forgot to set the prefix and when I set it, it started rebuilding from rustc_codegen_ssa onward.