[clang] [clang][AMDGPU] Clean-up handling of named barrier type (PR #207687)

[Pierre van Houtryve via cfe-commits]

Pierre-vh wrote:

> So I think it is better to diagnose this as unsupported in Clang for AMD SPIR-V for now, unless we also add explicit translator support.

I added a diagnostic for it

https://github.com/llvm/llvm-project/pull/207687