Strange behavior of OpenGLUT

["ldries46" <bertus.dries@planet.nl>]

I am using Open GL in one of my programs therefore I do include the Open GL 
library, the open GLU library and the Open Glut library
with the following calls:

with OpenGL; use OpenGL;
with OpenGL.GLU; use OpenGL.GLU;
with OpenGL.GLUT; use OpenGL.GLUT;

I show the strange behavior by the next code:

procedure display is -- chanced: GLvoid display( GLvoid );
begin
    glClear( GL_COLOR_BUFFER_BIT ); --correctly compiled
    ShowAxis;
    Wall;
    drawTriangles;
   glFlush;                                              --correctly 
compiled
   glutSwapBuffers;                               --NOT correctly compiled
end display;

then I get the following error message:

undefined reference to 'glutSwapBuffers'

while in the OpenGL.Glut package the following is presented:

   procedure glutSwapBuffers;

All calls to OpenGL.Glut subprograms in the file are found to have the same 
error but every variable from this file is correctly compiled
All calls op OpenGL subprograms are also correctly compiled.

I am using the OpenGL-glut.ads  by David Holm 2002-2003

What do I have to do to get this correctly compiled using GNAT GPS 2012

L. Dries