[llvm] [SVE ACLE] Add `NodeMap[V]` for `svcount` in SelectionDAGBuilder (PR #126089)

[Matt Arsenault via llvm-commits]

arsenm wrote:

Description needs to be fixed, I don't understand the point of this and commit message reading shouldn't require parsing through some other thread 

https://github.com/llvm/llvm-project/pull/126089