[llvm] [coro][pgo] Don't promote pgo counters in the suspend basic block (PR #71263)

[Mircea Trofin via llvm-commits]

mtrofin wrote:

> should the minimal spanning tree code use this interface too? 

Good idea - done. It needed a little rework - in the MST case we want to work with edges and block splitting the suspend faux edge. In the coro promotion case, we care about the basic block, and the property that none of the incoming edges is a faux suspend edge.

https://github.com/llvm/llvm-project/pull/71263