[llvm] [DAGCombiner] Add support for scalarising extracts of a vector setcc (PR #116031)

[David Sherwood via llvm-commits]

david-arm wrote:

Fixed failing test and pushed some of the opcode-related checks from `scalarizeExtractedBinOpCommon` into their callers.

https://github.com/llvm/llvm-project/pull/116031