On Fedora Linux:
$ MAKEOBJDIRPREFIX=~/obj tools/build/make.py -i TARGET=powerpc TARGET_ARCH=powerpc64 --cross-bindir=/usr/bin/ -j8 kernel-toolchain
$ MAKEOBJDIRPREFIX=~/obj tools/build/make.py -i TARGET=powerpc TARGET_ARCH=powerpc64 --cross-bindir=/usr/bin/ -j8 buildkernel