[clang] [CIR] Upstream CIR codegen for palignr x86 builtins (PR #173788)

[Amr Hesham via cfe-commits]

================
@@ -1,27 +1,18 @@
 // RUN: %clang_cc1 -x c -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx2 -fclangir -emit-cir -o %t.cir -Wall -Werror
 // RUN: FileCheck --check-prefixes=CIR --input-file=%t.cir %s
-// RUN: %clang_cc1 -x c -flax-vector-conversions=none -ffreestanding %s -triple=x86_64-unknown-linux -target-feature +avx2 -fno-signed-char -fclangir -emit-cir -o %t.cir -Wall -Werror
-// RUN: FileCheck --check-prefixes=CIR --input-file=%t.cir %s
----------------
AmrDeveloper wrote:

We can't remove old tests because they don't work with our new tests.

With the lit test, you can set a different prefix for each one `--check-prefixes=`, for example

```
CIR: 
CIR-NSC:
```

You can also set a common prefix for both cases

https://github.com/llvm/llvm-project/pull/173788