BUILD: makefile: reorder object files by build time

BUILD: makefile: reorder object files by build time

mux_spop is quite long to build and was at the end. The rest did not
change much, but the build time is now dominated by hlua.o and mux_h2.o
and by a large margin. On the 80-core ARM mux_h2.o is present from
beginning to end and on the PC it's hlua.o, so both might have to be
split at some point to benefit from multi-core.

Nevertheless, the changes allowed to shrink about one second out of
the 18 it was taking on that machine.