Move a lot of boilerplate to macros.shim
    
    There's a bunch of boilerplate to determine filenames and such based on
    which arch we're on; there's no reason to read it most of the time.
    Move all that to macros.shim.
    
    This makes the actual spec much more reasonable.
    
    Signed-off-by: Peter Jones <pjones@redhat.com>