[llvm] [llvm][GlobalOpt] Optimize statically resolvable IFuncs (PR #80606)

[Jon Roelofs via llvm-commits]

jroelofs wrote:

And here's an end-to-end example where it would apply: https://clang.godbolt.org/z/PYx6jT4W5

https://github.com/llvm/llvm-project/pull/80606