AMD k8 family does not support SSE4.x which are required by x86-64-v2+

So don't define __tune__k8__ for these micro architecture.

SSE, SSE2 and SSE3 appear in https://www.amd.com/system/files/TechDocs/25112.PDF
but not SSE4.x.

Differential Revision: https://reviews.llvm.org/D104116