It is not sufficient to check that the CPU supports the necessary
instructions. Also the operating system (or virtual machine hypervisor)
must enable all the AVX registers to be saved and restored on a
context switch.

Because clang 8 does not support the compiler intrinsic _xgetbv()
we will require clang 9 or later for enabling the use of VPCLMULQDQ
and the related AVX512 features.