[X86] Remove -mcpu=skx/knl from some tests and use -mattr instead.

mcpu exposes other tuning flags. These tests are only trying to test instruction set features so it is better to use mattr.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@330196 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed