[clang] [Clang/AMDGPU] Zero sized arrays not allowed in HIP device code. (PR #113470)

[Jon Chesterfield via cfe-commits]

https://github.com/JonChesterfield approved this pull request.

Error looks good. Might want to add a case for "dynamic __shared__" to the test file as the syntax is very close to the case being diagnosed - iirc it's things like

```cuda
extern __shared__ float array[];
```

Some existing handling in C like languages conflates `[]` and `[0]`, so might also want `extern __shared__ float array2[0];`

That's probably already covered by existing HIP test cases though, so if everything else is passing I think we're good. Thanks!

https://github.com/llvm/llvm-project/pull/113470