Function sysroot_remap 

fn sysroot_remap(
    build_runner: &BuildRunner<'_, '_>,
    unit: &Unit,
) -> (PathBuf, String)

Path prefix remap rules for sysroot.

This remap logic aligns with rustc: https://github.com/rust-lang/rust/blob/c2ef3516/src/bootstrap/src/lib.rs#L1113-L1116