[clang] [llvm] [NVPTX] Fix scoped atomic when given runtime values (PR #185883)

[Lewis Crawford via cfe-commits]

LewisCrawford wrote:

Could you clarify what you mean by "singlethreaded scope doesn't exist" here? As far as I can tell, it is only atomics, fences etc. where it is invalid. It should still be a valid sync-scope for volatile or non-atomic loads/stores though. Not sure if this just needs a clarifying comment and updating the commit message, or whether "singlethreaded" should be valid in getLLVMSyncScopeStr, but promoted to a wider scope elsewhere only for atomics, fences etc. where it is invalid on NVPTX.

It looks like https://github.com/llvm/llvm-project/pull/106101 adds the NVPTX support for this, so CCing @gonzalobg as the export on NVPTX SyncScopes.

https://github.com/llvm/llvm-project/pull/185883