Actually, this would seem to be a linux-headers bug - it seems that it should include the arch/powerpc/lib/crtsavres.o file or no modules will be able to be built against the kernel. Moving to linux-ports, the source of your linux-headers package.
You could probably work around this by installing the linux-source package, ensuring that you have write access to the unpacked kernel tree, and ensuring the /lib/modules/linux-$(uname -r)/source symlink points at the kernel tree.
Actually, this would seem to be a linux-headers bug - it seems that it should include the arch/powerpc/ lib/crtsavres. o file or no modules will be able to be built against the kernel. Moving to linux-ports, the source of your linux-headers package.
You could probably work around this by installing the linux-source package, ensuring that you have write access to the unpacked kernel tree, and ensuring the /lib/modules/ linux-$ (uname -r)/source symlink points at the kernel tree.