build: add an empty config.sh

This helper script will contain variables with results of configure
checks, so other scripts can source it.

Source it automatically in test-functions.sh, so every test can already
make use of it.

config.sh.in

@@ -0,0 +1,20 @@
+#!/bin/bash -
+# (C) Copyright 2019 Red Hat Inc.
+# @configure_input@
+#
+# 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 2 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, write to the Free Software
+# Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+# This shell script contains the results of some configure checks,
+# mostly used in other shell scripts.