Exclude SharedArray::SharedArrayHeader from the C++ docs

api/sixtyfps-cpp/include/sixtyfps_sharedarray.h

@@ -71,6 +71,7 @@ private:
         }
     }
 
+#if !defined(DOXYGEN)
     // Unfortunately, this cannot be generated by cbindgen because std::atomic is not understood
     struct SharedArrayHeader {
         std::atomic<std::intptr_t> refcount;
@@ -79,5 +80,6 @@ private:
     };
     static_assert(alignof(T) <= alignof(SharedArrayHeader), "Not yet supported because we would need to add padding");
     SharedArrayHeader *inner;
+#endif
 };
 }