Fix : libcanfestival_unix.a not built if examples are not compiled

Problem: when building Canfestival with unix timers 'libcanfestiva_unix.a'
is built only if you build examples too.

Test case:

$ ./configure --timers=unix --can=socket --target=unix
$ make canfestival

...

no errors but 'libcanfestival_unix.a' is not built:
$ find . -name "*.a"
./src/libcanfestival.a

Changing line 90 of 'drivers/unix/Makefile.in' to:
#driver: $(OBJS)
driver: libcanfestival_$(TARGET).a

solves the problem:

$ ./configure --timers=unix --can=socket --target=unix
$ make canfestival

...

$ find . -name "*.a"
./drivers/unix/libcanfestival_unix.a
./src/libcanfestival.a

#!/bin/sh

module="test_copcican_comedi"
device="test_copcican_comedi"
mode="664"

# insert neccessary modules
/sbin/insmod ../../drivers/can_copcican_comedi/can_copcican_comedi.ko
/sbin/insmod ../../src/canfestival.ko

# insert module with all arguments we got
# and use a pathname, as newer modutils don't look in . by default
/sbin/insmod ./$module.ko $* || exit 1

# stale nodes and device files are created by COMEDI

rmmod $module
rmmod canfestival
rmmod can_copcican_comedi