[clang] [llvm] [clang][SPIR-V] Add support for AMDGCN flavoured SPIRV (PR #89796)

[Alexey Bader via cfe-commits]

https://github.com/bader commented:

I'm okay with the patch in general, but I'd like either @michalpaszkowski or @VyacheslavLevytskyy to take a look.
Just one question about doubling the test scope for LLVM tests with spir64 target triple.

https://github.com/llvm/llvm-project/pull/89796