[clang] [Clang][AMDGPU] Add the missing builtin `__builtin_amdgcn_sqrt_bf16` (PR #149447)

[Shilei Tian via cfe-commits]

shiltian wrote:

### Merge activity

* **Jul 18, 12:42 PM UTC**: A user started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/149447).


https://github.com/llvm/llvm-project/pull/149447