pacify the parallel compiler

src/librustc_hir/hir.rs

@@ -667,7 +667,7 @@ impl Crate<'_> {
     where
         V: itemlikevisit::ParItemLikeVisitor<'hir> + Sync + Send,
     {
-        rustc_data_structures::parallel!(
+        parallel!(
             {
                 par_for_each_in(&self.items, |(_, item)| {
                     visitor.visit_item(item);

src/librustc_hir/lib.rs

@@ -6,6 +6,10 @@
 #![feature(const_fn)]
 #![feature(in_band_lifetimes)]
 #![feature(specialization)]
+#![recursion_limit = "256"]
+
+#[macro_use]
+extern crate rustc_data_structures;
 
 pub mod def;
 pub mod def_id;