Format hir_id_validator error using pretty print

Author: spastorino

compiler/rustc_passes/src/hir_id_validator.rs

@@ -103,7 +103,7 @@ impl<'a, 'hir> HirIdValidator<'a, 'hir> {
             self.error(|| {
                 format!(
                     "ItemLocalIds not assigned densely in {}. \
-                Max ItemLocalId = {}, missing IDs = {:?}; seens IDs = {:?}",
+                Max ItemLocalId = {}, missing IDs = {:#?}; seens IDs = {:#?}",
                     self.hir_map.def_path(owner).to_string_no_crate_verbose(),
                     max,
                     missing_items,