[clang] [Clang] Introduce scoped variants of GNU atomic functions (PR #72280)

[Matt Arsenault via cfe-commits]

================
@@ -205,6 +220,56 @@ class AtomicScopeHIPModel : public AtomicScopeModel {
   }
 };
 
+/// Defines the generic atomic scope model.
+class AtomicScopeGenericModel : public AtomicScopeModel {
+public:
+  /// The enum values match predefined built-in macros __ATOMIC_SCOPE_*.
+  enum ID {
+    System = 0,
+    Device = 1,
+    Workgroup = 2,
+    Wavefront = 3,
+    Single = 4,
+    Last = Single
+  };
+
+  AtomicScopeGenericModel() = default;
+
+  SyncScope map(unsigned S) const override {
+    switch (static_cast<ID>(S)) {
+    case Device:
+      return SyncScope::DeviceScope;
+    case System:
+      return SyncScope::SystemScope;
+    case Workgroup:
+      return SyncScope::WorkgroupScope;
+    case Wavefront:
+      return SyncScope::WavefrontScope;
+    case Single:
+      return SyncScope::SingleScope;
+    }
+    llvm_unreachable("Invalid language sync scope value");
----------------
arsenm wrote:

Maybe it would be better to just assume anything else is system?

https://github.com/llvm/llvm-project/pull/72280