The 3.5 release notes confirm that GC is not currently supported: "Things that don't work: - Objective-C garbage collection" This bug requests that such support be added. GC support was added in 10.5 and its use is spreading in 10.6. In 10.6, it is even sometimes required, for example when building 64 bit preference panes.
In the intervening 14 years, Objective-C garbage collection has been deprecated and then removed from macOS. This ticket should just be closed.
Happy to oblige!