[X86] Implement getHostCPUFeatures for X86.

Plan to use this as part of CPU 'native' support so we can stop picking a different CPU name if CPU doesn't support AVX or AVX2.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@233487 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed