[llvm] [Coroutines][LazyCallGraph] resumes are not really SCC (PR #116285)

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

The (Ref)SCCs must be accurate in regards to the actual IR. `addSplitRefRecursiveFunctions()` I believe only has the restriction that the new split functions are each in their own SCC but are in the same RefSCC, meaning they have (potentially indirect) circular references between all the split functions that are all ref edges, but they don't necessarily have to all reference each other directly.

If we have multiple split functions and one of them doesn't reference any of the others, there's `addSplitFunction()` for that case, and any remaining ref-recursive functions can be added with `addSplitRefRecursiveFunctions()`

https://github.com/llvm/llvm-project/pull/116285