[clang] [clang][HIP] Normalize __cdecl on abstract function types to the device default CC on amdgcnspirv (PR #210882)

[Mariya Podchishchaeva via cfe-commits]

https://github.com/Fznamznon commented:

Yep, this is what I meant. Thank you for prototyping this. 
@tahonermann , could you please take a look from SYCL perspective?

https://github.com/llvm/llvm-project/pull/210882