SSE2 path uses SSE4.1 intrinsic about bytecount

[Freaky]

Confused as to why it nonetheless works on a very old machine that tops out at "SSE4a", I look at a disassembly and find:

0000000000057b40 <core::core_arch::x86::sse41::_mm_extract_epi32>:
core::core_arch::x86::sse41::_mm_extract_epi32:
57b40:       8b 47 08                mov    eax,DWORD PTR [rdi+0x8]
57b43:       c3                      ret

..

0000000000057b50 <core::core_arch::x86::sse41::_mm_extract_epi32>:
core::core_arch::x86::sse41::_mm_extract_epi32:
   57b50:   8b 07                   mov    eax,DWORD PTR [rdi]
   57b52:   c3                      ret

So instead of an SSE4.1 pextrd, it actually compiled down to a couple of mov instructions. It seems unfortunate to depend on that.