Allow creation and modification of scopes in GN.

tools/gn/function_foreach.cc

Index: tools/gn/function_foreach.cc
diff --git a/tools/gn/function_foreach.cc b/tools/gn/function_foreach.cc
index d8fe87ed8c61be19638b688f137359bbfae5357e..c264e3c1ea83fdb3b6653b7166d261d7e84c2891 100644
--- a/tools/gn/function_foreach.cc
+++ b/tools/gn/function_foreach.cc
@@ -95,7 +95,8 @@ Value RunForEach(Scope* scope,
   if (old_loop_value_ptr) {
     // Put back old value. Use the copy we made, rather than use the pointer,
     // which will probably point to the new value now in the scope.
-    scope->SetValue(loop_var, old_loop_value, old_loop_value.origin());
+    scope->SetValue(loop_var, std::move(old_loop_value),
+                    old_loop_value.origin());
   } else {
     // Loop variable was undefined before loop, delete it.
     scope->RemoveIdentifier(loop_var);