[clang] [llvm] [SPIRV][RFC] Rework / extend support for memory scopes (PR #106429)

[Dmitry Sidorov via cfe-commits]

MrSidims wrote:

Tagging @svenvh to be aware of the discussion. I personally don't have a strong opinion at the moment of what should be a default. Currently [SPIR-V To LLVM translator](https://github.com/KhronosGroup/SPIRV-LLVM-Translator) picks "Device" as the default (translation of the atomic scope was added in this [PR](https://github.com/KhronosGroup/SPIRV-LLVM-Translator/pull/2222)), it's not necessarily correct, but I do believe that SPIR-V Backend and the translator must be aligned, and if Backend picks another default - the translator's implementation must be adjusted. 

https://github.com/llvm/llvm-project/pull/106429