libecore: tweak makekeys workaround for make 3.82

libecore: tweak makekeys workaround for make 3.82

It seems that make 3.82 gets confused and considers makekeys
out of date when there isn't a makekeys.o, so ensure that we
create both makekeys and makekeys.o before building.

Also move the workaround to the extract step so we can build using
make's default rules rather than explicitly calling gcc.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>