Function rustc_incremental::copy_cgu_workproduct_to_incr_comp_cache_dir

pub fn copy_cgu_workproduct_to_incr_comp_cache_dir(
    sess: &Session, 
    cgu_name: &str, 
    path: &Option<PathBuf>
) -> Option<(WorkProductId, WorkProduct)>

Copies a CGU work product to the incremental compilation directory, so next compilation can find and reuse it.