Always compile hir_id_validator.

Making this compilation conditional causes an unused crate dependency
warning.

Author: cjgillot

compiler/rustc_passes/src/lib.rs

@@ -23,7 +23,6 @@ mod debugger_visualizer;
 mod diagnostic_items;
 pub mod entry;
 mod errors;
-#[cfg(debug_assertions)]
 pub mod hir_id_validator;
 pub mod input_stats;
 mod lang_items;