[clang] [Clang] Permit `-Xarch_` to be used with `--offload-arch` (PR #131884)

[Alexey Bader via cfe-commits]

bader wrote:

> Like SPIRV is doing `nvidia_gpu_sm_89` instead of just `-Xarch_nvptx64 --offload-arch=sm_89`.

Like SYCL?

https://github.com/llvm/llvm-project/pull/131884