FileExistsError only available in Python 3.3+

FileExistsError is used here:
[torch/utils/ffi__init__.py](https://github.com/pytorch/pytorch/blob/e034f258e358898adfacf2f3ac08ab278a5117ee/torch/utils/ffi/__init__.py#L82)
but it is not available in the 2.7.x targets, only 3.3+.
