Fix GL/GLU detection on older distributions

This resolves Bug 2155

Signed-off-by: François Andriot <francois.andriot@free.fr>

ConfigureChecks.cmake

@@ -297,13 +297,23 @@ if( WITH_OPENGL )
       tde_message_fatal( "opengl is requested and found, but it doesn't provides glXChooseVisual() or GL/glx.h" )
     endif( )
   else( )
-    tde_message_fatal( "opengl is requested, but not found on your system" )
+    check_library_exists( GL glXChooseVisual "" HAVE_GLXCHOOSEVISUAL )
+    if( HAVE_GLXCHOOSEVISUAL )
+      set( GL_LIBRARIES "GL" )
+    else( HAVE_GLXCHOOSEVISUAL )
+      tde_message_fatal( "opengl is requested, but not found on your system" )
+    endif( HAVE_GLXCHOOSEVISUAL )
   endif( )
 
   if( BUILD_KCONTROL )
     pkg_search_module( GLU glu )
     if( NOT GLU_FOUND )
-      tde_message_fatal( "glu is required, but not found on your system" )
+      check_library_exists( GLU gluGetString "" HAVE_GLUGETSTRING )
+      if( HAVE_GLUGETSTRING )
+        set( GLU_LIBRARIES "GLU" )
+      else( HAVE_GLUGETSTRING )
+        tde_message_fatal( "glu is required, but not found on your system" )
+      endif( HAVE_GLUGETSTRING )
     endif( )
   endif( BUILD_KCONTROL )