message: miniheap: use broadly compatable atomic<> notation
diff: @@ -306,8 +306,8 @@ protected:
  internal::BinToken _token;
  Freelist<MaxFreelistLen> _freelist;
  const uint16_t _objectSize;
  - atomic_uint16_t _inUseCount{0};
  - mutable atomic_uint16_t _refCount{0};
  + atomic<uint16_t> _inUseCount{0};
  + mutable atomic<uint16_t> _refCount{0};
  uint8_t _meshCount : 7;
  uint8_t _attached : 1;
  internal::Bitmap _bitmap;
  