Fix compilation ofrtl/nds/classes.pp unit

rtl/nds/classes.pp

@@ -15,6 +15,7 @@
  **********************************************************************}
 
 {$mode objfpc}
+{$IF FPC_FULLVERSION>=30301}
 {$modeswitch FUNCTIONREFERENCES}
 {$define FPC_HAS_REFERENCE_PROCEDURE}
 {$endif}