[clang] [NFC][docs][HIP] Update HIP docs around `hipstdpar` and SPIR-V (PR #124803)

[Alex Voicu via cfe-commits]

AlexVlx wrote:

> LLVM Buildbot has detected a new failure on builder `openmp-offload-libc-amdgpu-runtime` running on `omp-vega20-1` while building `clang` at step 7 "Add check check-offload".
> 
> Full details are available at: https://lab.llvm.org/buildbot/#/builders/73/builds/12605
> 
> Here is the relevant piece of the build log for the reference

This looks like a pure fluke, there’s no interaction between this docs only change and the failing test.

https://github.com/llvm/llvm-project/pull/124803