bpo-33041: Fix downcast warning on Windows

[vstinner]

Cast pointer difference from ssize_t to int: a frame is very unlikely
larger than 2 GB.

https://bugs.python.org/issue33041

[vstinner]

I'm not sure about silently downcasting ssize_t to int. Maybe a check at runtime would be safer, but I'm too lazy to write complex code to handle errors :-) What do you think @serhiy-storchaka? Is it ok to rely that a stack will not be larger than 2 GB?

[serhiy-storchaka]

I think it is safe. This difference should be limited by co_stacksize which has type int.

[vstinner]

I think it is safe. This difference should be limited by co_stacksize which has type int.

Oh right. Thanks for checking!

[bedevere-bot]

@vstinner: Please replace # with GH- in the commit message next time. Thanks!