[PyQt] SIP 4.19+ and private destructors

[Raphael Kubo da Costa]

After sip change 1688:71a8ee38b2c6 ("Fixed a regression in determining
when a shadow class should be generated") I'm having problems with
QObject-derived classes that define a private destructor.

For example, the following excerpt:

  %Module C
  %Import QtCore/QtCoremod.sip
  class C : public QObject {
  private:
    ~C();
  };

generates a "class sipC : public  ::C", that fails to build because C's
destructor is private. Before that change, sip would just generate code
creating and manipulating C directly.

Was that intentional or is this an actual bug?