In MacPorts, a BSD package manager for open software on Macs, the problem has been discussed in a few tickets or bug reports. The problem is that particularly Mac OS X 10.4 or "Tiger" and Mac OS X 10.5 or "Leopard" (since Mac OS X 10.6 or "Snow Leopard" the situation seems to have changed, but I have no proof at hand) need to use unnamed semaphores, which is first time discussed here: https://trac.macports.org/ticket/56185. Since I wanted to have GnuPG working on Tiger and Leopard with gpg-agent I created a set of patches and described this here: https://trac.macports.org/ticket/61115. This ticket provides the necessary patch and other files.
With the release of version 1.7 a new change is needed: https://trac.macports.org/ticket/69517. Gpg-agent works at least on Tiger, Mac OS X 10.4.11.
Does it make sense to make an old Mac OS X aware release?