Merge branch 'refs/heads/t/build_system'

Merge branch 'refs/heads/t/build_system'

Cooking for more than a month.

* t/build_system:
  Add message to target maintainer-clean.
  Use git version for tarball and AC_INIT().
  Run autom4te instead of autoconf.
  Remove depend.sh.
  Simplify make clean.
  Do not create .d files for gengetopt source files.
  Introduce cmdlist_dir.
  Remove pointless autoconf checks.
  Avoid excessive dep generation on Makefile changes.
  Add -Wformat to STRICT_CFLAGS.
  Compile with -Wall -Wunused only on linux.
  Separate CPPFLAGS and CFLAGS.
  Rename DEBUG_CPPFLAGS to STRICT_CFLAGS.
  Only compile with osl_cppflags where necessary.
  Remove pointless -r option to cp for target tarball.
  Make tarball commands quiet.
  Do not opencode $(tarball).
  Run tr only once in configure.ac.
  Silence ggo_descriptions_declared command.
  Call AC_CONFIG_HEADERS rather than AM_CONFIG_HEADER.
  Remove duplicate -Wno-unused-function.
  Honor --with-xxx-headers also for dependencies.