galileo: Add support for old versions of GNU Make
galileo: Add support for old versions of GNU Make

This patch revises a Makefile to avoid using a feature that is
incompatible with GNU Make v.3.81.

MohamedSeliem/contiki,arurke/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki,arurke/contiki,MohamedSeliem/contiki,arurke/contiki,arurke/contiki,MohamedSeliem/contiki,arurke/contiki,arurke/contiki,arurke/contiki,MohamedSeliem/contiki,MohamedSeliem/contiki