[NativeCPU] Fix build after IRBuilder::CreateIntrinsic change in vecz
Adapt to CreateIntrinsic now returning Value* instead of CallInst* by
storing the result and using cast<CallInst> before returning.
Similar to ca7828cc93c3e which fixed the same issue in SPIRV translator.
Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>