[llvm] [VectorCombine] Pull out TargetCostKind argument to allow globally set cost kind value (PR #118652)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

> Sounds OK to me. Did you consider making it a class member, to avoid all the extra args to the fold functions?

That would be easy enough to do - I wasn't sure if we needed the flexibility of a per-function call instead or not though.

https://github.com/llvm/llvm-project/pull/118652