[X86] Add avx512vl and avx512dq command lines to combine-pmuldq.ll to demonstrate...

[X86] Add avx512vl and avx512dq command lines to combine-pmuldq.ll to demonstrate where we fail to use pmuldq/pmuludq and use to pmullq instead.

It's nice that pmullq exists, but it has higher latency and probably lower throughput than pmuldq/pmuludq. We should prefer those if we can.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@321436 91177308-0d34-0410-b5e6-96231b3b80d8