tests should link to -lrt explicitly

[James Hunt]

The test cases should explicitly link to -lrt since this is required for job_process.c and is already specified when building init itself.

Seen on arm:

Making check in init
make[3]: Entering directory `/home/jhunt/upstart-1.6.1/init'
make TERM=xterm check-am
make[4]: Entering directory `/home/jhunt/upstart-1.6.1/init'
make TERM=xterm test_system test_environ test_process test_job_class test_job_process test_job test_log test_state test_event test_event_operator test_blocked test_parse_job test_parse_conf test_conf test_control
make[5]: Entering directory `/home/jhunt/upstart-1.6.1/init'
  CC test_system.o
  CCLD test_system
  CC test_environ.o
  CCLD test_environ
  CC test_process.o
  CC test_util.o
  CCLD test_process
job_process.c:1774: error: undefined reference to 'clock_gettime'
collect2: error: ld returned 1 exit status
make[5]: *** [test_process] Error 1
make[5]: Leaving directory `/home/jhunt/upstart-1.6.1/init'
make[4]: *** [check-am] Error 2
make[4]: Leaving directory `/home/jhunt/upstart-1.6.1/init'
make[3]: *** [check] Error 2
make[3]: Leaving directory `/home/jhunt/upstart-1.6.1/init'
make[2]: *** [check-recursive] Error 1
make[2]: Leaving directory `/home/jhunt/upstart-1.6.1'
dh_auto_test: make -j1 check returned exit code 2
make[1]: *** [override_dh_auto_test] Error 29
make[1]: Leaving directory `/home/jhunt/upstart-1.6.1'
make: *** [build-arch] Error 2

[Tuomo Tanskanen (tuomotanskanen)]

Duplicate of https://bugs.launchpad.net/upstart/+bug/918570 but since you resolved this one already, marking the original bug as duplicate of this.