Method mark_abi_exports

src/build.rs:397–401

(manifest: &BuildManifest, assembled: &mut AssembledOutput)

            plan,
            units,
            linked,
        })
    }

    // Program/extra objects and any object defining an entry symbol are roots.
    fn prune_unreferenced_stdlib(
        units: Vec<BuiltUnit>,
        prunable: &std::collections::HashSet<String>,