Binaries without AVX512 kernels shouldn't report CPU Capability as AVX512 on machines with AVX512 support (#66703)
Summary:
### BUG
If a PyTorch binary is built with a compiler that doesn't support all the AVX512 intrinsics in the codebase, then it won't have ATen AVX512 kernels, but at runtime, CPU capability would still be incorrectly returned as AVX512 on a machine that supports AVX512. It seems that PyTorch Linux releases are done on CentOS with `gcc 7.3`, so this bug would manifest in the 1.10 release, unless a fix such as this one is added. gcc versions below 9.0 don't support all the AVX512 intrinsics in the codebase, such as `_mm512_set_epi16`.
### FIX
CPU Capability would be returned as AVX512 at runtime only if the binary was built with a compiler that supports all the AVX512 intrinsics in the codebase, and if the hardware the binary is being run on supports all the required AVX512 instruction sets.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66703
Reviewed By: gchanan
Differential Revision: D31732625
Pulled By: malfet
fbshipit-source-id: e52d06b87fbe2af9b303a2e9c264189c8512d5ec
