Outdated libtool creates trouble on macOS

[Torbjörn Granlund]

Marc Glisse <marc.glisse at inria.fr> writes:

  Do you think we could increase AC_PREREQ to 2.70 (or even 2.71), which
  would allow a couple more cleanups? I don't think we want to support
  users rerunning autoconf with an older version than the one we use to
  generate the tarballs.

Sure.  Being compatible with older versions than what we use seems quite
unnecessary.

-- 
Torbjörn
Please encrypt, key id 0xC8601622