Move functor to its own namespace to block bringing boost::core to ADL.

include/boost/core/functor.hpp

@@ -18,6 +18,9 @@
 
 namespace boost::core {
 
+// Block unintended ADL
+namespace functor_ns {
+
 //! A function object that invokes a function specified as its template parameter
 template< auto Function >
 struct functor
@@ -29,6 +32,10 @@ struct functor
     }
 };
 
+} // namespace functor_ns
+
+using functor_ns::functor;
+
 } // namespace boost::core
 
 #endif // BOOST_CORE_FUNCTOR_HPP