Attach TokenStream to ast::Block

A `Block` does not have outer attributes, so we only capture tokens when
parsing a `macro_rules!` matcher

compiler/rustc_builtin_macros/src/deriving/mod.rs

@@ -75,6 +75,7 @@ fn call_intrinsic(
         id: ast::DUMMY_NODE_ID,
         rules: ast::BlockCheckMode::Unsafe(ast::CompilerGenerated),
         span,
+        tokens: None,
     }))
 }