[X86][AVX] Added codegen tests for _mm256_zext* helper intrinsics (PR32839)

Not great codegen, especially as VEX moves support implicit zeroing of upper bits....

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301748 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed