Move storage of final vtbl from BaseClass to IrInterface: BaseClass instances are shared! Always use the target's irstruct interfaceMap when building the const initializer. Tango helloworld works again.

// idouble

module typeinfo1.ti_idouble;

private import typeinfo1.ti_double;

class TypeInfo_p : TypeInfo_d
{
    char[] toString() { return "idouble"; }
}