Tweak print_attr_item.

This commit rearranges the `match`. The new code avoids testing for
`MacArgs::Eq` twice, at the cost of repeating the `self.print_path()`
call. I think this is worthwhile because it puts the `match` in a more
standard and readable form.

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -469,16 +469,17 @@ fn print_attr_item(&mut self, item: &ast::AttrItem, span: Span) {
                 true,
                 span,
             ),
-            MacArgs::Empty | MacArgs::Eq(..) => {
+            MacArgs::Empty => {
+                self.print_path(&item.path, false, 0);
+            }
+            MacArgs::Eq(_, token) => {
                 self.print_path(&item.path, false, 0);
-                if let MacArgs::Eq(_, token) = &item.args {
                 self.space();
                 self.word_space("=");
                 let token_str = self.token_to_string_ext(token, true);
                 self.word(token_str);
             }
         }
-        }
         self.end();
     }