Compute has_pub_restricted in the resolver.

compiler/rustc_resolve/src/build_reduced_graph.rs

@@ -265,6 +265,8 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
                 })
             }
             ast::VisibilityKind::Restricted { ref path, id, .. } => {
+                // Make `PRIVATE_IN_PUBLIC` lint a hard error.
+                self.r.has_pub_restricted = true;
                 // For visibilities we are not ready to provide correct implementation of "uniform
                 // paths" right now, so on 2018 edition we only allow module-relative paths for now.
                 // On 2015 edition visibilities are resolved as crate-relative by default,