use matches!() macro in more places

compiler/rustc_builtin_macros/src/proc_macro_harness.rs

@@ -256,10 +256,7 @@ impl<'a> Visitor<'a> for CollectProcMacros<'a> {
         // we're just not interested in this item.
         //
         // If we find one, try to locate a `#[proc_macro_derive]` attribute on it.
-        let is_fn = match item.kind {
-            ast::ItemKind::Fn(..) => true,
-            _ => false,
-        };
+        let is_fn = matches!(item.kind, ast::ItemKind::Fn(..));
 
         let mut found_attr: Option<&'a ast::Attribute> = None;