When building Cuirass with 'guix build -f build-aux/guix.scm' we don't want to
add "build-aux/guix.scm" in the repository snapshot since it is considered as
metadata. As a consequence we can't make 'autoconf' require it.
* configure.ac (AC_REQUIRE_AUX_FILE): Remove "build-aux/guix.scm".
* Makefile.am (EXTRA_DIST): Only distribute it.
* build-aux/git-version-gen: New script.
* configure.ac (AC_INIT): Use it.
(AC_REQUIRE_AUX_FILE): Distribute it.
* Makefile.am (.version): New target.
(BUILT_SOURCES, EXTRA_DIST): Add it.
(dist-hook): Generate ".tarball-version".
* .gitignore: Update.
* Makefile.am (src/cuirass/config.scm, $(go_files)): New targets.
(do_subst, generate_file, go_files): New variables.
(EXTRA_DIST): Distribute 'src/cuirass/config.scm.in'.
(DISTCLEANFILES): Rename to ...
(MOSTLYCLEANFILES): ... this.
* configure.ac (AC_CONFIG_FILES): Remove 'src/cuirass/config.scm'.
(@expanded_datadir@, @expanded_localstatedir@): Delete.
(AC_PROG_MKDIR_P, AC_PROG_SED): Use them.
* src/cuirass/config.scm (%datadir): Set it to $(localstatedir).
(%localstatdir): Set it to $(datadir).