[clang] [Clang][HIP] Deprecate __hip_atomic_* builtins (PR #189897)

[Sameer Sahasrabuddhe via cfe-commits]

ssahasra wrote:

The latest change makes the deprecation `DefaultIgnore` and puts it in a new group that can be enabled with `-Whip-deprecated-builtins`. This allows this patch to be committed without affecting existing ROCM headers. Once I have separately cleaned up all the uses of these builtins inside ROCM, we can turn this warning on by default and put a deprecation schedule in place.

https://github.com/llvm/llvm-project/pull/189897