[llvm] [FoldingSet] Switch to linear probing and Algorithm R deletion (PR #218190)

[Nikita Popov via llvm-commits]

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

LGTM

This seems like the most straightforward baseline implementation. Further changes (like whether to have a separate hash array to avoid dereferencing the node) can be based on top of it and evaluated in isolation from the main change.

https://github.com/llvm/llvm-project/pull/218190