Fix split calculation in type alias where clauses

Author: stuuupidcat

compiler/rustc_parse/src/parser/item.rs

@@ -1024,7 +1024,7 @@ impl<'a> Parser<'a> {
                 has_where_token: after_where_clause.has_where_token,
                 span: after_where_clause.span,
             },
-            split: before_where_clause.predicates.len(),
+            split: before_where_clause.predicates.iter().filter(|p| p.attrs.is_empty()).count(),
         };
         let mut predicates = before_where_clause.predicates;
         predicates.extend(after_where_clause.predicates);