Making the fixdep helper to be invoked within dep-cmd.

Each user of the build framework needs to make sure fixdep exists before
executing the build itself.

If the build doesn't find fixdep, it falls back to the old style
dependency tracking.
Signed-off-by: NJiri Olsa <jolsa@kernel.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1443004442-32660-6-git-send-email-jolsa@kernel.orgSigned-off-by: NArnaldo Carvalho de Melo <acme@redhat.com>