Don't re-collect tokenstream twice to pretty print

src/librustc_metadata/encoder.rs

@@ -1316,7 +1316,7 @@ fn encode_info_for_macro_def(&mut self, macro_def: &hir::MacroDef) -> Entry<'tcx
         let def_id = self.tcx.hir().local_def_id(macro_def.hir_id);
         Entry {
             kind: EntryKind::MacroDef(self.lazy(&MacroDef {
-                body: pprust::tts_to_string(&macro_def.body.trees().collect::<Vec<_>>()),
+                body: pprust::tokens_to_string(macro_def.body.clone()),
                 legacy: macro_def.legacy,
             })),
             visibility: self.lazy(&ty::Visibility::Public),