Missing implementation of xsimd::kernel::detail::interleave for AVX2

[ni-eddiemond]

The function xsimd::kernel::detail::interleave does not seem to be implemented for AVX2. It is however present in the SSE4.1 header. It would be great if the AVX2 header would not depend on the SSE4.1 header to be included beforehand but to be self-sufficient instead.
I get a compilation error because of this. I'm using with MSVC 17.12.2

xsimd/include/xsimd/arch/xsimd_avx2.hpp

Line 744 in 0252ae7

constexpr int imask = detail::interleave(mask);