rollup merge of #21340: pshc/libsyntax-no-more-ints

Collaboration with @rylev!

I didn't change `int` in the [quasi-quoter](99ae1a30f3/src/libsyntax/ext/quote.rs (L328)), because I'm not sure if there will be adverse effects.

Addresses #21095.

src/librustc/lint/builtin.rs

@@ -1329,7 +1329,7 @@ impl UnusedMut {
                 let ident = path1.node;
                 if let ast::BindByValue(ast::MutMutable) = mode {
                     if !token::get_ident(ident).get().starts_with("_") {
-                        match mutables.entry(ident.name.uint()) {
+                        match mutables.entry(ident.name.usize()) {
                             Vacant(entry) => { entry.insert(vec![id]); },
                             Occupied(mut entry) => { entry.get_mut().push(id); },
                         }

src/librustc/util/ppaux.rs

@@ -164,7 +164,7 @@ pub fn explain_region_and_span(cx: &ctxt, region: ty::Region)
     fn explain_span(cx: &ctxt, heading: &str, span: Span)
                     -> (String, Option<Span>) {
         let lo = cx.sess.codemap().lookup_char_pos_adj(span.lo);
-        (format!("the {} at {}:{}", heading, lo.line, lo.col.to_uint()),
+        (format!("the {} at {}:{}", heading, lo.line, lo.col.to_usize()),
          Some(span))
     }
 }