The latest version of XCode allows you to specify separate settings for x86 & PPC code, although it isn’t really obvious how to do it. After some digging I figured it out.
Some of the build settings such as SDKROOT & GCC_VERSION allow you to specify which architecture they apply to by appending _ppc or _i386 to the settings name. Here’s how I’m able to build a universal binary that will run on OS X 10.2 or later (which requires it to be built with GCC 3.3) as well as x86.
First, set up the project & target settings as required for building the x86 version. Then add the following variables to the build panel of the project or target settings window (hit the ‘+’ button to add a variable & edit the name).
MACOSX_DEPLOYMENT_TARGET_ppc 10.2 GCC_VERSION_ppc 3.3 SDKROOT_ppc /Developer/SDKs/MacOSX10.2.8.sdk
Those settings will override the defaults when building a PPC binary, while the defaults will be used when building x86.
Architecture-dependent build settings aren't new. I can confirm that SDKROOT was able to be tweaked in 2.1 already, and probably years before; earlier documentation refers to it as a way to compile for ppc64 (the G5), now 30 months old. (However, I don't know if MACOSX_DEPLOYMENT_TARGET and GCC_VERSION are available on these older versions.)
GCC_VERSION is new, and it's the key. Before that, you were stuck with separate build passes for gcc 4.0 and 3.3 on Intel/PPC, respectively, and lipo afterwards. Or, you could have done this unsupported hack,