Doesn't arm need the machine link too?
At the very least, it should be not-harmful.
I can understand making the x86 link be extra only on x86... There should be a standard way to do that, but sadly there isn't.

On arm we use the standard headers from buildworld. I suspect this is here to allow loader to be built directly on an older world, i.e. without using buildenv. As I'm mostly cross building, so will be using buildenv to test, this is less of an issue on arm.

In D2283#5, @andrew wrote:

On arm we use the standard headers from buildworld. I suspect this is here to allow loader to be built directly on an older world, i.e. without using buildenv. As I'm mostly cross building, so will be using buildenv to test, this is less of an issue on arm.

Once upon a time, you could cd to any boot directory on the native architecture and type 'make' and have it work, even if you hadn't already built world. This seems to break it for arm.

Definitely amd64 to ${MACHINE_CPUARCH} is a good change. I'm indifferent to the other changes but regardless of which way we go here I'd expect loader and boot1 to be the same.

I agree with Warner that it would be nice to keep the 'cd boot/foo && make' compatibility without requiring buildenv.