Don't try get local DefId of imported macro in rustdoc.

src/librustdoc/doctree.rs

@@ -233,9 +233,11 @@ pub struct DefaultImpl {
     pub whence: Span,
 }
 
+// For Macro we store the DefId instead of the NodeId, since we also create
+// these imported macro_rules (which only have a DUMMY_NODE_ID).
 pub struct Macro {
     pub name: Name,
-    pub id: ast::NodeId,
+    pub def_id: hir::def_id::DefId,
     pub attrs: hir::HirVec<ast::Attribute>,
     pub whence: Span,
     pub matchers: hir::HirVec<Span>,