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.

lib/Makefile.am

@@ -0,0 +1,28 @@
+## Makefile for the lib subdirectory of GNU gperf.
+## Copyright (C) 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
+## the Free Software Foundation; either version 3 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+## Process this file with automake to produce Makefile.in.
+
+AUTOMAKE_OPTIONS = 1.11 foreign
+
+noinst_LIBRARIES = libgp.a
+libgp_a_SOURCES = \
+  getopt.h getopt.c getopt1.c \
+  getline.h getline.cc \
+  hash.h hash.cc
+
+EXTRA_DIST = \
+  filename.h