[VectorCombine] Add tests for UB issue, remove immediate UB from existing tests. NFC#138395

lukel97 merged 1 commit intollvm:mainllvm/llvm-project:mainfrom

lukel97:vector-combine/scalarize-ub-testslukel97/llvm-project:vector-combine/scalarize-ub-testsCopy head branch name to clipboard