[X86] Improve the unknown stepping support for Intel CPUs in getHostCPUName
[X86] Improve the unknown stepping support for Intel CPUs in getHostCPUName

This patch improves our guessing of unknown Intel CPUs to support Goldmont and skylake-avx512.

Differential Revision: https://reviews.llvm.org/D35161

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@309246 91177308-0d34-0410-b5e6-96231b3b80d8

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