[llvm] [ADT] SCC iterator for general graph (PR #84268)

[Yida Zhang via llvm-commits]

zyd2001 wrote:

I think we can say in the doc that `scc_iterator` is for CFG like graph since it only performs Tarjar's DFS based algorithm from single entry point, so it won't produce correct result for generic graph.

https://github.com/llvm/llvm-project/pull/84268