[clang] [Clang] Mark scoped_atomics with !noalias.addrspace(private) (PR #230044)

[via cfe-commits]

easyonaadit wrote:

>From the [spec](https://rocm.docs.amd.com/projects/HIP/en/latest/how-to/hip_cpp_language_extensions.html#atomic-functions): 
```
Atomic operations in kernels can operate on block scope (i.e. shared memory), 
device scope (global memory), or system scope (system memory), 
depending on [hardware support](https://rocm.docs.amd.com/projects/HIP/en/latest/reference/hardware_features.html).
```
-- not on thread private memory.

https://github.com/llvm/llvm-project/pull/230044