[clang] Add clang atomic control options and attribute (PR #114841)

[Artem Belevich via cfe-commits]

================
@@ -1093,6 +1097,169 @@ inline void FPOptions::applyChanges(FPOptionsOverride FPO) {
   *this = FPO.applyOverrides(*this);
 }
 
+/// Atomic control options
+class AtomicOptionsOverride;
+class AtomicOptions {
+public:
+  using storage_type = uint16_t;
+
+  static constexpr unsigned StorageBitSize = 8 * sizeof(storage_type);
+
+  static constexpr storage_type FirstShift = 0, FirstWidth = 0;
+#define OPTION(NAME, TYPE, WIDTH, PREVIOUS)                                    \
+  static constexpr storage_type NAME##Shift =                                  \
+      PREVIOUS##Shift + PREVIOUS##Width;                                       \
+  static constexpr storage_type NAME##Width = WIDTH;                           \
+  static constexpr storage_type NAME##Mask = ((1 << NAME##Width) - 1)          \
+                                             << NAME##Shift;
+#include "clang/Basic/AtomicOptions.def"
+
+  static constexpr storage_type TotalWidth = 0
+#define OPTION(NAME, TYPE, WIDTH, PREVIOUS) +WIDTH
+#include "clang/Basic/AtomicOptions.def"
+      ;
+  static_assert(TotalWidth <= StorageBitSize,
+                "Too short type for AtomicOptions");
+
+private:
+  storage_type Value;
+
+  AtomicOptionsOverride getChangesSlow(const AtomicOptions &Base) const;
+
+public:
+  AtomicOptions() : Value(0) {
+    setNoRemoteMemory(false);
+    setNoFineGrainedMemory(false);
+    setIgnoreDenormalMode(false);
+  }
+  explicit AtomicOptions(const LangOptions &LO) {
+    Value = 0;
+#if 0
----------------
Artem-B wrote:

What's the plan for the ifdefed-out lines?

https://github.com/llvm/llvm-project/pull/114841