For the non-Nuitka case, use the new form of of module initialization, changing the module init() function to call PyModuleDef_Init() providing an exec()-function as slot to be called for each subinterpreter, For the Nuitka case, maintain the old code path and call the exec() function directly, as Nuitka does not seem to support it yet. At the moment, the lazy initialization code is called from the exec() function. Full subinterpreter support requires further investigation on how to make lazy initialization work with multiple binterpreters. [ChangeLog][shiboken6] Multi-phase Python extension module initialization is now used for the non-deployed case. Task-number: PYSIDE-3155 Task-number: PYSIDE-2221 Change-Id: Ie55953d47354b8f832d935fe42a686739dbce2ca Reviewed-by: Shyamnath Premnadh <Shyamnath.Premnadh@qt.io>