[doc] fix another doxygen friendliness issue

diff --git a/include/simgrid/s4u/Io.hpp b/include/simgrid/s4u/Io.hpp
index 8ac6040..50cf48d 100644 (file)
--- a/include/simgrid/s4u/Io.hpp
+++ b/include/simgrid/s4u/Io.hpp
@@ -34,9 +34,11 @@ private:
   explicit Io(sg_storage_t storage, sg_size_t size, OpType type);
 
 public:
+#ifndef DOXYGEN
   friend XBT_PUBLIC void intrusive_ptr_release(simgrid::s4u::Io* i);
   friend XBT_PUBLIC void intrusive_ptr_add_ref(simgrid::s4u::Io* i);
   friend Storage; // Factory of IOs
+#endif
 
   ~Io() = default;