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.

lib/configure.ac

@@ -23,7 +23,7 @@ AC_PREREQ([2.70])
 AC_INIT([gperf], [package])
 AC_CONFIG_SRCDIR([hash.cc])
 AC_CONFIG_AUX_DIR([../build-aux])
-AC_CONFIG_MACRO_DIRS([../m4])
+AC_CONFIG_MACRO_DIRS([gnulib-m4])
 VERSION_NUMBER=`sed -n -e 's/.*version_string = "\(.*\)".*/\1/p' < $srcdir/../src/version.cc`
 gl_INIT_PACKAGE_VERSION([$VERSION_NUMBER])
 AM_INIT_AUTOMAKE
@@ -35,10 +35,14 @@ AC_PROG_CC
                       dnl sets variable CC
 AC_PROG_CXX
                       dnl sets variable CXX
+gl_EARLY
+                      dnl Early macro expansions from gnulib
 AC_CHECK_TOOL([AR], [ar])
                       dnl sets variable AR
 AC_PROG_RANLIB
                       dnl sets variable RANLIB
+gl_INIT
+                      dnl Main macro expansions from gnulib
 dnl
 dnl           That's it.
 dnl