Autotools 2.70

Autotools 2.70 have enabled warning by default for obsolete constructs:

*** Warnings about obsolete constructs are now on by default.

  These warnings can be turned off with ‘-Wno-obsolete’.

  Many of these warnings advise maintainers to run autoupdate.
  Be aware that autoupdate cannot solve all backward compatibility
  problems, and cannot completely solve all of the problems it does
  address.  A configure script edited by autoupdate is likely to
  need further manual fix-ups.

(from https://lwn.net/Articles/839395/)

We should fix those:

❯ autoreconf
configure.ac:72: warning: The macro `AC_CONFIG_HEADER' is obsolete.
configure.ac:72: You should run autoupdate.
./lib/autoconf/status.m4:719: AC_CONFIG_HEADER is expanded from...
configure.ac:72: the top level
configure.ac:98: warning: The macro `AC_HELP_STRING' is obsolete.
configure.ac:98: You should run autoupdate.
./lib/autoconf/general.m4:203: AC_HELP_STRING is expanded from...
./lib/autoconf/general.m4:1533: AC_ARG_ENABLE is expanded from...
configure.ac:98: the top level
configure.ac:105: warning: The macro `AC_HELP_STRING' is obsolete.
configure.ac:105: You should run autoupdate.
./lib/autoconf/general.m4:203: AC_HELP_STRING is expanded from...
./lib/autoconf/general.m4:1533: AC_ARG_ENABLE is expanded from...
configure.ac:105: the top level
configure.ac:112: warning: The macro `AC_HELP_STRING' is obsolete.
configure.ac:112: You should run autoupdate.
./lib/autoconf/general.m4:203: AC_HELP_STRING is expanded from...
./lib/autoconf/general.m4:1533: AC_ARG_ENABLE is expanded from...
configure.ac:112: the top level
[...]