dh-autoreconf/autotools-dev questions

[Oohara Yuuma <oohara@libra.interq.or.jp>]

I am packaging a software which uses autoconf and automake.  I will
regenerate all autotool files with dh-autoreconf.
* The upstream tarball contains auto-generated files.  Do I have to
  save these files somewhere before calling dh_autoreconf and restore
  them in the clean target, or is it enough to remove auto-generated
  files in the clean target so that they are regenerated again
  in the build target? 
* The software doesn't use AC_CANONICAL or libtool.  Running autoreconf
  manually doesn't generate config.{guess, sub}.  Do I have to
  build-depend on autotools-dev and call both dh_autoreconf and
  dh_autotools-dev_updateconfig to copy the latest config.{guess, sub},
  or is it enough to set the --build and --host options of configure
  with dpkg-architecture?

-- 
Oohara Yuuma <oohara@libra.interq.or.jp>