X86: fold SSE2/AVX2 logical shift by immediate amount into zero vector when possible

Patch by Andrea Di Biagio


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186165 91177308-0d34-0410-b5e6-96231b3b80d8
Add static.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186170 91177308-0d34-0410-b5e6-96231b3b80d8