[llvm] [IPO] Added attributor for identifying invariant loads (PR #141800)

[Krzysztof Drewniak via llvm-commits]

https://github.com/krzysz00 approved this pull request.

I think this is good from what I can tell.

Although one ask - either here in or in a followup PR - can we make sure that this still works with `ptr addrspace(7)`s created by `make.buffer.rsrc.p7.p1`? (Or that stuff like `invariant.start` doesn't break the analysis?)

https://github.com/llvm/llvm-project/pull/141800