Add compare_exchange_deleter to DataPtr/UniqueVoidPtr (#16513)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16513
compare_exchange_deleter makes it easier to replace a
deleter on a DataPtr with a new one, without requiring
allocating another closure to hold the old deleter.
See comment for details.
This diff was originally landed as part of D13762540
(#16226) but we are reverting that diff D13863610 (#16510)
Reviewed By: smessmer
Differential Revision: D13864245
fbshipit-source-id: 56eda4748238dd3a5130ba6434fda463fe7c690e
