In the spirit of ff56954b, fix the
build of linuxboot.S with old as(1) (as found in some BSD base systems)
by emitting the bytes of the insn it doesn't like instead.

Signed-off-by: Juergen Lock <nox@jelal.kn-bremen.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>