rustdoc: Fix cross-crate macro source links

The source filename for cross crate macros isn't quite right so the normal
generated links are invalid.

Closes #21311

src/librustdoc/html/static/main.js

@@ -802,6 +802,9 @@
     if (query['gotosrc']) {
         window.location = $('#src-' + query['gotosrc']).attr('href');
     }
+    if (query['gotomacrosrc']) {
+        window.location = $('.srclink').attr('href');
+    }
 
     $("#expand-all").on("click", function() {
         $(".docblock").show();