Attach tokens to ast::Stmt

We currently only attach tokens when parsing a `:stmt` matcher for a
`macro_rules!` macro. Proc-macro attributes on statements are still
unstable, and need additional work.

compiler/rustc_builtin_macros/src/deriving/debug.rs

@@ -133,5 +133,5 @@ fn stmt_let_underscore(cx: &mut ExtCtxt<'_>, sp: Span, expr: P<ast::Expr>) -> as
         span: sp,
         attrs: ast::AttrVec::new(),
     });
-    ast::Stmt { id: ast::DUMMY_NODE_ID, kind: ast::StmtKind::Local(local), span: sp }
+    ast::Stmt { id: ast::DUMMY_NODE_ID, kind: ast::StmtKind::Local(local), span: sp, tokens: None }
 }