build: Use gnulib-tool with a module list.

* .gitmodules: New file.
* gitsub.sh: New file, from gnulib/top/gitsub.sh.
* autopull.sh: Use gitsub.sh to check out gnulib.
* autogen.sh: Accept --skip-gnulib option. Invoke gnulib-tool, assuming
a gnulib checkout is already present.
* Makefile.devel (lib/aclocal.m4): Update reference to macros directory.
* lib/configure.ac: Likewise. Invoke gl_EARLY, gl_INIT.
* lib/Makefile.am (EXTRA_DIST, MOSTLYCLEANFILES): New variables.
Include Makefile.gnulib.

autogen.sh

@@ -21,8 +21,61 @@
 # You should have received a copy of the GNU General Public License
 # along with this program.  If not, see <https://www.gnu.org/licenses/>.
 
-# Prerequisite (if not used from a released tarball): ./autopull.sh
-# Usage: ./autogen.sh
+# Prerequisite (if not used from a released tarball): either
+#   - the GNULIB_SRCDIR environment variable pointing to a gnulib checkout, or
+#   - a preceding invocation of './autopull.sh'.
+#
+# Usage: ./autogen.sh [--skip-gnulib]
+#
+# Options:
+#   --skip-gnulib       Avoid fetching files from Gnulib.
+#                       This option is useful
+#                       - when you are working from a released tarball (possibly
+#                         with modifications), or
+#                       - as a speedup, if the set of gnulib modules did not
+#                         change since the last time you ran this script.
+
+skip_gnulib=false
+while :; do
+  case "$1" in
+    --skip-gnulib) skip_gnulib=true; shift;;
+    *) break ;;
+  esac
+done
+
+if test $skip_gnulib = false; then
+
+  if test -n "$GNULIB_SRCDIR"; then
+    test -d "$GNULIB_SRCDIR" || {
+      echo "*** GNULIB_SRCDIR is set but does not point to an existing directory." 1>&2
+      exit 1
+    }
+  else
+    GNULIB_SRCDIR=`pwd`/gnulib
+    test -d "$GNULIB_SRCDIR" || {
+      echo "*** Subdirectory 'gnulib' does not yet exist. Use './gitsub.sh pull' to create it, or set the environment variable GNULIB_SRCDIR." 1>&2
+      exit 1
+    }
+  fi
+  # Now it should contain a gnulib-tool.
+  GNULIB_TOOL="$GNULIB_SRCDIR/gnulib-tool"
+  test -f "$GNULIB_TOOL" || {
+    echo "*** gnulib-tool not found." 1>&2
+    exit 1
+  }
+  GNULIB_MODULES='
+    filename
+    package-version
+  '
+  $GNULIB_TOOL --lib=libgp --source-base=lib --m4-base=lib/gnulib-m4 \
+    --makefile-name=Makefile.gnulib \
+    --import \
+    $GNULIB_MODULES
+  $GNULIB_TOOL --copy-file build-aux/install-sh; chmod a+x build-aux/install-sh
+  $GNULIB_TOOL --copy-file build-aux/mkinstalldirs; chmod a+x build-aux/mkinstalldirs
+  $GNULIB_TOOL --copy-file build-aux/compile; chmod a+x build-aux/compile
+  $GNULIB_TOOL --copy-file build-aux/ar-lib; chmod a+x build-aux/ar-lib
+fi
 
 make -f Makefile.devel totally-clean all || exit $?