[X86] Remove brand_id check from getHostCPUName.

Brand index was a feature some Pentium III and Pentium 4 CPUs.
It provided an index into a software lookup table to provide a
brand name for the CPU. This is separate from the family/model.

It's unclear to me why this index being non-zero was used to
block checking family/model. I think the effect of this is that
-march=native was not working correctly on the CPUs that have a
non-zero brand index. They are all about 20 years old so this
probably hasn't affected many users.