[SLP]Gather scalarized calls
If the calls won't be vectorized, but will be scalarized after
vectorization, they should be build as buildvector nodes, not vector
nodes. Vectorization of such calls leads to incorrect cost estimation,
does not allow to calculate correctly spills costs.
Reviewers: lukel97, preames
Reviewed By: preames
Pull Request: https://github.com/llvm/llvm-project/pull/125070
