[clang] [CIR][X86] Add support for kunpck builtins (PR #168757)

[Andy Kaylor via cfe-commits]

andykaylor wrote:

> > You've lost the test in your latest update.
> 
> i don't think we need to add new tests since they already exist please check the following reply [#168757 (comment)](https://github.com/llvm/llvm-project/pull/168757#discussion_r2546450816)

Oh, sorry. I gave you the wrong path in my comment requesting that you move the tests you originally added. The test should be added to `clang/test/CIR/CodeGen/X86/avx512f-builtins.c` (my original comment missed the `CIR` part of the path). The existing tests cover the classic codegen for these builtins. We need new tests to test them with `-fclangir`.

https://github.com/llvm/llvm-project/pull/168757