@edef Sorry, should have specified - I'm targeting PowerPC Darwin, which I believe is not possible.
@edef GCC's much better in general at targeting obsolete architectures - for unsurprising reasons. I've also been poking at a potential project targeting SuperH, which is still supported in GCC - meaning it's possible to build a toolchain supporting the latest C and C++ standards, with better optimization than was available in compilers of its day.