makefiles writing to $@ should first write to $@.new

There are many Makefile rules like

foo: bar
    ./tool $< > $@

If the rule is interrupted (due to ^C or ENOSPC), foo can be 0 bytes or
partially written, but won't be rebuilt until someone runs distclean or debugs
it and removes the individual file, as I did for errcodes.h.

It'd be better if these did

./tool $< > $@.new
mv $@.new $@

-- 
Justin