bpo-30598: _PySys_EndInit() now duplicates warnoptions

[vstinner]

Fix a reference in subinterpreters, like test_callbacks_leak() of
test_atexit.

warnoptions is a list used to pass options from the command line to
the sys module constructor. Before this change, the list was shared
by multiple interpreter which is not the expected behaviour. Each
interpreter should have their own independent mutable world.

This change duplicates the list in each interpreter. So each
interpreter owns its own list, so each interpreter can clear its own
list.

[ncoghlan]

This makes sense to me - PEP 432 has the config setting eventually moving into the main interpreter config struct, and then each interpreter instance should have its own copy drawn from that original.

[vstinner]

This makes sense to me - PEP 432 has the config setting eventually moving into the main interpreter config struct, and then each interpreter instance should have its own copy drawn from that original.

For me, the current global variable is only here to pass the initial value. Once sys is created, I don't expect that the global variable and sys.warnoptions are linked anymore. If you modify the global variable after sys creation, it should do nothing. Well, in practice, it will affect the newly created subinterpreters.

And now replace "global variable" with "config" ;-)