This time, my system is running the now-old 10.5 (Leopard) using Xcode 3.1.4. I'm probably the only one who wants to build on 10.5, but I still appreciate the fact that GHC can be built on a variety of systems, allowing more people (like me) to hack on it.
FWIW it worked, including gmp, about 6 months ago when I built GHC 7 and the Haskell Platform from source on my old iBook (RIP). It was somewhat amusing having a newer and better-working GHC setup on the iBook than on the desktop (SL and GHC 6.10.4 from MacPorts).