[clang] [llvm] AMDGPU: Add gfx950 subtarget definitions (PR #116307)

[Matt Arsenault via cfe-commits]

arsenm wrote:

### Merge activity

* **Nov 18, 1:34 PM EST**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/116307).


https://github.com/llvm/llvm-project/pull/116307