[llvm] [StatepointLowering] Take return attributes of `gc.result` into account (PR #68439)

[via llvm-commits]

dantrushin wrote:

LGTM, but I think @annamthomas or @danilaml should really look at this.
Ping me for explicit approval if they won't respond in few days.

https://github.com/llvm/llvm-project/pull/68439