Rollup merge of #58096 - h-michael:linkchecker-2018, r=Centril

Transition linkchecker to 2018 edition

Transition `src/tools/linkchecker` to Rust 2018.

#58099

src/tools/linkchecker/Cargo.toml

@@ -2,6 +2,7 @@
 name = "linkchecker"
 version = "0.1.0"
 authors = ["Alex Crichton <alex@alexcrichton.com>"]
+edition = "2018"
 
 [[bin]]
 name = "linkchecker"

src/tools/linkchecker/main.rs

@@ -14,6 +14,8 @@
 //! A few whitelisted exceptions are allowed as there's known bugs in rustdoc,
 //! but this should catch the majority of "broken link" cases.
 
+#![deny(rust_2018_idioms)]
+
 use std::collections::hash_map::Entry;
 use std::collections::{HashMap, HashSet};
 use std::env;
@@ -21,7 +23,7 @@ use std::fs;
 use std::path::{Path, PathBuf, Component};
 use std::rc::Rc;
 
-use Redirect::*;
+use crate::Redirect::*;
 
 macro_rules! t {
     ($e:expr) => (match $e {