Also use typename on clang. This is the same fix as the previous one.

That code will still not work should someone use -std=c++03 on clang
and a more substantial fix should be done.

Arrangement_on_surface_2/include/CGAL/Curved_kernel_via_analysis_2/Arc_2.h

@@ -3234,7 +3234,7 @@ public:
         return  is_equal(arc2);
     }
 
-#if defined(_MSC_VER)
+#if defined(_MSC_VER) || defined(__clang__)
     // befriending the kernel point
     friend typename Curved_kernel_via_analysis_2::Point_2;