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

[Vyacheslav Levytskyy via cfe-commits]

VyacheslavLevytskyy wrote:

> > @AlexVlx I don't see much objections against #108528 on a conceptual level, so what do you think about merging it into this PR in a way that I commented above, by changing `getMemScope()` and moving `getOrInsertSyncScopeID()` into its static vars initialization?
> 
> At a glance it seems fine, thank you for working through this, but since I've been away for a couple of days let me page things back in first:)

Sure, it's just that some parts of the discussion may be irrelevant if you'd choose the https://github.com/llvm/llvm-project/pull/108528 approach :)

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