Add warn(unreachable_pub) to rustc_type_ir.

Author: nnethercote

Diff for: compiler/rustc_type_ir/src/fold.rs

@@ -354,7 +354,7 @@ struct Shifter<I: Interner> {
 }
 
 impl<I: Interner> Shifter<I> {
-    pub fn new(cx: I, amount: u32) -> Self {
+    fn new(cx: I, amount: u32) -> Self {
         Shifter { cx, current_index: ty::INNERMOST, amount }
     }
 }

Diff for: compiler/rustc_type_ir/src/lib.rs

@@ -6,6 +6,7 @@
 )]
 #![cfg_attr(feature = "nightly", allow(internal_features))]
 #![cfg_attr(not(bootstrap), allow(rustc::usage_of_type_ir_inherent))]
+#![warn(unreachable_pub)]
 // tidy-alphabetical-end
 
 extern crate self as rustc_type_ir;