Add warn(unreachable_pub) to rustc_mir_build.

Author: nnethercote

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -993,7 +993,7 @@ impl UnsafeOpKind {
     }
 }
 
-pub fn check_unsafety(tcx: TyCtxt<'_>, def: LocalDefId) {
+pub(crate) fn check_unsafety(tcx: TyCtxt<'_>, def: LocalDefId) {
     // Closures and inline consts are handled by their owner, if it has a body
     // Also, don't safety check custom MIR
     if tcx.is_typeck_child(def.to_def_id()) || tcx.has_attr(def, sym::custom_mir) {

compiler/rustc_mir_build/src/lib.rs

@@ -8,6 +8,7 @@
 #![feature(if_let_guard)]
 #![feature(let_chains)]
 #![feature(try_blocks)]
+#![warn(unreachable_pub)]
 // tidy-alphabetical-end
 
 mod build;