We decide what dwarf unwind to choose way after the Makefile.feature
makefile is included. The $(dwarf-post-unwind) is not even set at that
time. For the same reason it was never included in FEATURE-DUMP file.

Moving it into perf VF=1 verbose display.

  $ make VF=1
    BUILD:   Doing 'make -j4' parallel build
  Auto-detecting system features:
  ...                         dwarf: [ on  ]
  ...
  ...                 LIBUNWIND_DIR:
  ...                     LIBDW_DIR:
  ...     DWARF post unwind library: libunwind
  ...
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Wang Nan <wangnan0@huawei.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Zefan Li <lizefan@huawei.com>
Cc: pi3orama <pi3orama@163.com>
Link: http://lkml.kernel.org/r/1450893514-9158-3-git-send-email-jolsa@kernel.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>