Fix dangling reference in Construct_center_3(Circle_3)

Cartesian_kernel/include/CGAL/Cartesian/Circle_3.h

@@ -130,12 +130,12 @@ class CircleC3 {
     return diametral_sphere();
   }
 
-  Point_3 center() const
+  decltype(auto) center() const
   {
     return diametral_sphere().center();
   }
 
-  FT squared_radius() const
+  decltype(auto) squared_radius() const
   {
     return diametral_sphere().squared_radius();
   }
@@ -155,7 +155,7 @@ class CircleC3 {
     return CGAL_PI * CGAL_PI * 4.0 * to_double(squared_radius());
   }
 
-  FT area_divided_by_pi() const
+  decltype(auto) area_divided_by_pi() const
   {
     return squared_radius();
   }

Cartesian_kernel/include/CGAL/Cartesian/Sphere_3.h

@@ -163,6 +163,7 @@ typename R::Oriented_side
 SphereC3<R>::
 oriented_side(const typename SphereC3<R>::Point_3_ &p) const
 {
+  typedef typename R::Oriented_side Oriented_side;
   return enum_cast<Oriented_side>(bounded_side(p)) * orientation();
 }
 
@@ -172,6 +173,7 @@ typename R::Bounded_side
 SphereC3<R>::
 bounded_side(const typename SphereC3<R>::Point_3_ &p) const
 {
+  typedef typename R::Bounded_side Bounded_side;
   return enum_cast<Bounded_side>(compare(squared_radius(),
                                          squared_distance(center(), p)));
 }

Cartesian_kernel/include/CGAL/Cartesian/Tetrahedron_3.h

@@ -143,7 +143,7 @@ oriented_side(const typename TetrahedronC3<R>::Point_3 &p) const
 {
   typename R::Orientation o = orientation();
   if (o != ZERO)
-    return enum_cast<Oriented_side>(bounded_side(p)) * o;
+    return enum_cast<typename R::Oriented_side>(bounded_side(p)) * o;
 
   CGAL_kernel_assertion (!is_degenerate());
   return ON_ORIENTED_BOUNDARY;