[llvm] [LLVM] Make s_getpc_b64 rematerializable (PR #71823)

[Nicolai Hähnle via llvm-commits]

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

Thanks for explaining. Acim, in general it would still be good to split this into two commits, but I suppose for this one it can go in as-is.

https://github.com/llvm/llvm-project/pull/71823