autoconf-archive: add new package (#15782)

var/spack/repos/builtin/packages/autoconf-archive/package.py

+# Copyright 2013-2020 Lawrence Livermore National Security, LLC and other
+# Spack Project Developers. See the top-level COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+
+class AutoconfArchive(AutotoolsPackage, GNUMirrorPackage):
+    """The GNU Autoconf Archive is a collection of more than 500 macros for
+    GNU Autoconf."""
+
+    homepage = "https://www.gnu.org/software/autoconf-archive/"
+    gnu_mirror_path = "autoconf-archive/autoconf-archive-2019.01.06.tar.xz"
+
+    version('2019.01.06', sha256='17195c833098da79de5778ee90948f4c5d90ed1a0cf8391b4ab348e2ec511e3f')