[rustbuild] Side-step HashMap iteration to preserve command-line step order.

src/bootstrap/step.rs

@@ -1217,8 +1217,8 @@ fn expand(&self, steps: &[Step<'a>]) -> Vec<Step<'a>> {
         let mut visited = HashSet::new();
         visited.insert(0);
         let idx_to_node = nodes.iter().map(|p| (*p.1, p.0)).collect::<HashMap<_, _>>();
-        for idx in nodes.values() {
-            self.topo_sort(*idx, &idx_to_node, &edges, &mut visited, &mut order);
+        for idx in 0..nodes.len() {
+            self.topo_sort(idx, &idx_to_node, &edges, &mut visited, &mut order);
         }
         return order
     }