Add warn(unreachable_pub) to rustc_passes.

compiler/rustc_passes/src/weak_lang_items.rs

@@ -15,7 +15,11 @@ use crate::errors::{
 
 /// Checks the crate for usage of weak lang items, returning a vector of all the
 /// lang items required by this crate, but not defined yet.
-pub fn check_crate(tcx: TyCtxt<'_>, items: &mut lang_items::LanguageItems, krate: &ast::Crate) {
+pub(crate) fn check_crate(
+    tcx: TyCtxt<'_>,
+    items: &mut lang_items::LanguageItems,
+    krate: &ast::Crate,
+) {
     // These are never called by user code, they're generated by the compiler.
     // They will never implicitly be added to the `missing` array unless we do
     // so here.