Turn current clean output:

  $ make clean
  rm -f arch/x86/include/generated/asm/syscalls_64.c
    CLEAN    libbpf
    CLEAN    libapi

into:

  $ make clean
    CLEAN    x86
    CLEAN    libapi
    CLEAN    libbpf
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: TJ <linux@iam.tj>
Link: http://lkml.kernel.org/r/1461615438-27894-1-git-send-email-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>