chore: import upstream snapshot with attribution

cmake/thread_safety_attributes.cpp

@@ -0,0 +1,25 @@
+#if defined(__clang__)
+#define THREAD_ANNOTATION_ATTRIBUTE_(x) __attribute__((x))
+#else
+#define THREAD_ANNOTATION_ATTRIBUTE_(x)
+#endif
+
+#define CAPABILITY(x) THREAD_ANNOTATION_ATTRIBUTE_(capability(x))
+#define ACQUIRE() THREAD_ANNOTATION_ATTRIBUTE_(acquire_capability())
+#define RELEASE() THREAD_ANNOTATION_ATTRIBUTE_(release_capability())
+
+class CAPABILITY("mutex") Mutex {
+ public:
+  void lock() ACQUIRE();
+  void unlock() RELEASE();
+};
+
+void Mutex::lock() ACQUIRE() {}
+void Mutex::unlock() RELEASE() {}
+
+int main() {
+  Mutex m;
+  m.lock();
+  m.unlock();
+  return 0;
+}