build: Use Automake in lib/.

* autopull.sh: Copy also m4/init-package-version.m4.
* autogen.sh: Mention the requirement for Automake.
* Makefile.devel (lib/aclocal.m4, lib/config.h.in, lib/Makefile.in): New
rules.
(lib/configure): Use lib/aclocal.m4 instead of the top-level aclocal.m4.
(src/config.h.in): Fix rule.
(totally-clean): Remove the new generated files.
* lib/configure.ac: Require Autoconf >= 2.70. Change AC_INIT invocation.
Invoke AC_CONFIG_MACRO_DIRS, gl_INIT_PACKAGE_VERSION, AM_INIT_AUTOMAKE,
AC_CONFIG_HEADERS. Don't invoke AC_MAKE_SET, AC_PROG_CPP,
AC_PROG_CXXCPP, AC_PROG_INSTALL.
* lib/Makefile.am: New file.
* lib/Makefile.in: Remove file.
* Makefile.in (IMPORTED_FILES): Remove lib/filename.h.

autopull.sh

@@ -7,7 +7,7 @@
 #     in a gnulib checkout, or
 #   - an internet connection.
 
-# Copyright (C) 2003-2022 Free Software Foundation, Inc.
+# Copyright (C) 2003-2025 Free Software Foundation, Inc.
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
@@ -28,6 +28,7 @@ GNULIB_REPO_URL="https://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=blob_plain;
 
 for file in build-aux/install-sh build-aux/mkinstalldirs \
             build-aux/compile build-aux/ar-lib \
+            m4/init-package-version.m4 \
             lib/filename.h; do
   if test -n "$GNULIB_TOOL"; then
     $GNULIB_TOOL --copy-file $file $file