build: Add config.scm.in.

* gash/config.scm.in:
* configure: Use it to generate gash/config.scm
* .gitignore: Ignore generated file.
* gash/gash.scm (display-version): Use it.
* build-aux/build-guile.sh: Compile it.

.gitignore

@@ -3,3 +3,4 @@
 /bin/gash
 /.config.make
 /doc/version.texi
+/gash/config.scm

build-aux/build-guile.sh

@@ -38,6 +38,7 @@ set -e
 SCM_FILES="
 gash/bournish-commands.scm
 gash/builtins.scm
+gash/config.scm
 gash/guix-build-utils.scm
 gash/gash.scm
 gash/io.scm

configure

@@ -40,6 +40,10 @@ SHELL=$BASH
 VERSION=$VERSION
 EOF
 
+sed \
+    -e "s,@VERSION@,$VERSION,"\
+    gash/config.scm.in > gash/config.scm
+
 cat <<EOF
 Run:
   make            to build gash

gash/config.scm.in

@@ -0,0 +1,30 @@
+;;; Gash -- Guile As SHell
+;;; Copyright © 2018 Jan (janneke) Nieuwenhuizen <janneke@gnu.org>
+;;;
+;;; This file is part of Gash.
+;;;
+;;; Gash 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.
+;;;
+;;; Gash 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 Gash.  If not, see <http://www.gnu.org/licenses/>.
+
+(define-module (gash config)
+  #:export (%version))
+
+;;; Commentary:
+;;;
+;;; Compile-time configuration of gash.  When adding a substitution variable
+;;; here, make sure to have configure substitute it.
+;;;
+;;; Code:
+
+(define %version
+  "@VERSION@")