[gtkada] Configure doesn't find openGL

[Emmanuel Briot]

> I can't get configure to produce a system that includes openGL.
> CC=/usr/bin/gcc ./configure LDFLAGS="-framework OpenGL -L/System/Library/Frameworks/OpenGL.framework/Libraries".

Take a look at the contents of config.log

I am not sure we really support openGL on OSX though (or that gtk+ itself
supports it correctly). The GLArea widget has not been updated in a while
on the C side.

Emmanuel