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

[Alex Voicu via cfe-commits]

AlexVlx wrote:

@bader @asudarsa @michalpaszkowski any opinions from the SPIRV side? I would like to merge this so as to be able to progress some related work, but I'd rather not squat on SPIRV real-estate without an ACK from the landlords:)

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