Build_Discriminated_Subtype may be invoked on a E_Record_Type_With_Private,
in which case it builds a E_Record_Subtype_With_Private which does not have
the Cloned_Subtype field.
gcc/ada/
PR ada/99020
* sem_ch3.adb (Build_Discriminated_Subtype): Set the Cloned_Subtype
only if the type is not private.