The newly added trace command requires an external audit library.

However it can cause a build error because it's not checked whether the
libaudit is installed on system:

    CC builtin-trace.o
  builtin-trace.c:7:22: fatal error: libaudit.h: No such file or directory
  compilation terminated.
  make: *** [builtin-trace.o] Error 1
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1348745018-21744-1-git-send-email-namhyung@kernel.org
[ committer note: Added ", disables 'trace tool' to the feature warning msg ]
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>