This isn't a question, yet, depending on replies. It's more of a good-news story (for me, anyway). I'm a hobbyist with legacy mac systems and pretty much a newbie with Sage commands per se, and wanted to use the experience to get a better handle on the structure and behavior of the build system. I just hope this adds to the mac build knowledge base for Sage.
I've just successfully built sage-6.10 (downloaded from the git repository) on a mac book 4,1 system with a Core2Duo processor that does not upgrade MacOS beyond Snow Leopard. The total build time was about 8 hours starting with Xcode 3.2. I had difficulties getting started because all my more modern tools are in my macports installation, and I haven't installed upgrades anywhere else --- or so I thought at first. I hit upon including the path to a previous Sage installation which I did some years ago with a binary download of sage-5.13, adding the path to Sage's local/bin. And it worked!
I had one glitch with the installation of flint-2.5.2, when its makefile died with a request to cp -a which happened after:
mkdir -p "./sage-6.10/local/lib"
mkdir -p "./sage-6.10/local/include/flint"
In my os x shell, there is no cp -a and I substituted cp -pPR by using the debug shell for the build system. Everything else went off without a hitch. What a marvelously robust build system this is, with a finicky set of standard mac build tools! Perhaps I should not find it remarkable that I can still do a build like this with a ten-or-more-year-old computer running a 12-year-old OS.