For Darwin ppc usage of uname -m breaks the build

[barracuda156]

uname -m gives out Power Macintosh, and that value fails to work. Either sensible uname -p should be used for both machine and arch, or otherwise explicit value is to be set. Passing --with-machine= or --with-force-machine= do not solve the problem: they let pass through configure stage, but then the build still breaks down since os.sh forces power macintosh as a dir name.