Dear Hiura, thanks a lot for your help.
I was finally able to compile OK with makefiles on mac.
The resulting screensaver, stopped having the problem with the garbage collection.
However, when I copied the .saver package to a mountain lion mac, I saw again the same error message, which probably means that mountain lion needs a different treatment for GC. That was a quick test, I cannot report more details right now. (I am working on window's part this period of time.)
Thanks again