[GtkGLExt] problem with g++

[merlin o mago <mbontorin gmail com>]

I have a probem with g++. When I compile a program that uses gtkglext
I get the following error:

user hostname:~/$ g++ `pkg-config --cflags --libs gtk+-2.0 gtkglext-1.0` gears.c
gears.c: In function `int main(int, char**)':
gears.c:470: error: invalid conversion from `int' to `GdkGLConfigMode'
gears.c:478: error: invalid conversion from `int' to `GdkGLConfigMode'

This always happens that I use glconfig and this problem doesn't occur with gcc.

The program gears is an example of gtkglext-1.0. How I could solve this problem?