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

[Arvind Sudarsanam via cfe-commits]

asudarsa wrote:

> 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.

+1 on this. I will take a look before end of week on this. Thanks

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