[i386] Replace builtins with vector extensions

[Kirill Yukhin]

Hello Marc,
On 26 Jul 19:34, Marc Glisse wrote:
> I did some AVX and AVX512F intrinsics, and it still passes the
> testsuite (on my old pre-AVX x86_64-linux-gnu).

I've performed testing of your patch using functional simulator of
AVX*. And see no regressions as well.

--
Thanks, K