[Bug target/83250] _mm256_zextsi128_si256 missing for AVX2 zero extension

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83250

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Intrinsics now implemented for GCC 10+, keeping open for some optimizations.