[clang] [Headers][X86] Allow SLLDQ/SRLDQ byte shift intrinsics to be used in constexpr (PR #164166)

[Simon Pilgrim via cfe-commits]

https://github.com/RKSimon requested changes to this pull request.

Missing _mm512_bslli_epi128 / _mm512_bsrli_epi128 test coverage in avx512bw-builtins.c

https://github.com/llvm/llvm-project/pull/164166