[llvm] [Statepoint] Treat result of atomicrmw xchg as a base pointer (PR #97280)

[Philip Reames via llvm-commits]

https://github.com/preames approved this pull request.

LGTM

Though, FYI, I haven't worked on this stuff for ~3 years at this point.  

https://github.com/llvm/llvm-project/pull/97280