[SLPVectorizer] Add basic support for mul/and/or/xor horizontal reductions

Expand arithmetic reduction to include mul/and/or/xor instructions.

This patch just fixes the SLPVectorizer - the effective reduction costs for AVX1+ are still poor (see rL344846) and will need to be improved before SLP sees this as a valid transform - but we can already see the effect on SSE2 tests.

This partially helps PR37731, but doesn't fix it all as it still falls over on the extraction/reduction order for some reason.

Differential Revision: https://reviews.llvm.org/D53473

llvm-svn: 345037