[X86] Workaround possible CPUID bug in Sandy Bridge. Don't access leaf 7 subleaf 1 unless subleaf 0 says it is supported via EAX. Intel documentation says invalid subleaves return 0. We had been relying on that behavior instead of checking the max sublef number. It appears that some Sandy Bridge CPUs return at least the subleaf 0 EDX value for subleaf 1. Best guess is that this is a bug in a microcode patch since all of the bits we're seeing set in EDX were introduced after Sandy Bridge was originally released. This is causing avxvnniint16 to be incorrectly enabled with -march=native on these CPUs. Reviewed By: pengfei, anna Differential Revision: https://reviews.llvm.org/D156963
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