[LLVM][GlobalISel] Make CSEMIRBuilder::buildConstant scalable vector aware.#158299

paulwalker-arm merged 2 commits intollvm:mainllvm/llvm-project:mainfrom

paulwalker-arm:vector-constants-global-isel-splatpaulwalker-arm/llvm-project:vector-constants-global-isel-splatCopy head branch name to clipboard