Needed to build Rust 1.86.0. With 1.84.1 it fails with:

       Compiling clap_complete v4.5.37
       Compiling build_helper v0.1.0 (/pkg/rustc-1.86.0-0/build/rustc-1.86.0-src/src/build_helper)
    error[E0658]: use of unstable library feature `io_error_more`
       --> src/bootstrap/src/utils/helpers.rs:150:31
        |
    150 |         Err(e) if e.kind() == io::ErrorKind::CrossesDevices => {
        |                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        |
        = note: see issue #86442 <https://github.com/rust-lang/rust/issues/86442> for more information
        = help: add `#![feature(io_error_more)]` to the crate attributes to enable
        = note: this compiler was built on 2025-01-27; consider upgrading it if it is out of date

    For more information about this error, try `rustc --explain E0658`.
    error: could not compile `bootstrap` (lib) due to 1 previous error
    failed to run: /usr/local/package/bin/cargo build --manifest-path /pkg/rustc-1.86.0-0/build/rustc-1.86.0-src/src/bootstrap/Cargo.toml -Zroot-dir=/pkg/rustc-1.86.0-0/build/rustc-1.86.0-src --frozen
    Build completed unsuccessfully in 0:00:27