[ruby/prism] Various cleanup with new -x option

https://github.com/ruby/prism/commit/020756fb11

prism/util/pm_newline_list.h

@@ -63,6 +63,8 @@ bool pm_newline_list_init(pm_newline_list_t *list, const uint8_t *start, size_t
 
 /**
  * Clear out the newlines that have been appended to the list.
+ *
+ * @param list The list to clear.
  */
 void
 pm_newline_list_clear(pm_newline_list_t *list);