[SelectionDAG] When legalizing the result type of CONCAT_VECTORS, take into...

[SelectionDAG] When legalizing the result type of CONCAT_VECTORS, take into account whether the input type also needs to be promoted.

If so go ahead and get the promoted input vector to extract from. Previously, we would create a bunch of any_extends of extract_vector_elts with illegal input type that needs to be promoted. The legalization of those extract_vector_elts would then potentially introduce a truncate. So now we have a bunch of any_extends of truncates. By legalizing both parts together we avoid creating these extra nodes.

The test changes seem to be because we were previously combining the build_vector with the any_extend before the any_extend got combined with the truncate.

llvm-svn: 320669