make extensions work with CVS autoconf

[Eric Blake]

Now that CVS autoconf has macros which use AC_USE_SYSTEM_EXTENSIONS, the code 
that generates gl_EARLY needs to take this into account.  For example, without 
this patch,

$ gnulib-tool --test fpending strlen
Module list with included dependencies:
  fpending
  strnlen
File list:
  lib/__fpending.c
  lib/__fpending.h
  lib/dummy.c
  lib/strnlen.c
  lib/strnlen.h
  m4/fpending.m4
  m4/onceonly_2_57.m4
  m4/strnlen.m4
executing autoreconf --force --install
configure.ac:35: warning: AC_COMPILE_IFELSE was called before 
AC_USE_SYSTEM_EXTENSIONS
../../lib/autoconf/specific.m4:415: AC_USE_SYSTEM_EXTENSIONS is expanded from...
../../lib/autoconf/functions.m4:1674: AC_FUNC_STRNLEN is expanded from...
glm4/strnlen.m4:22: gl_FUNC_STRNLEN is expanded from...
configure.ac:34: gl_INIT is expanded from...
configure.ac:35: the top level
configure.ac:35: warning: AC_RUN_IFELSE was called before 
AC_USE_SYSTEM_EXTENSIONS
configure.ac:35: warning: AC_COMPILE_IFELSE was called before AC_AIX
../../lib/autoconf/specific.m4:449: AC_AIX is expanded from...
configure.ac:35: warning: AC_RUN_IFELSE was called before AC_AIX
configure.ac:35: warning: AC_COMPILE_IFELSE was called before AC_MINIX
../../lib/autoconf/specific.m4:468: AC_MINIX is expanded from...
configure.ac:35: warning: AC_RUN_IFELSE was called before AC_MINIX
configure.ac:35: warning: AC_COMPILE_IFELSE was called before 
AC_USE_SYSTEM_EXTENSIONS
../../lib/autoconf/specific.m4:415: AC_USE_SYSTEM_EXTENSIONS is expanded from...
../../lib/autoconf/functions.m4:1674: AC_FUNC_STRNLEN is expanded from...
glm4/strnlen.m4:22: gl_FUNC_STRNLEN is expanded from...
configure.ac:34: gl_INIT is expanded from...
configure.ac:35: the top level

This patch is two-fold.  First, the strnlen module now depends on extensions, 
as otherwise it no longer installs any .m4 files for gnulib-tool to detect that 
extensions must be added to gl_EARLY.  Second, the extensions module needs to 
work with CVS autoconf.  Plus, it looks like the original extensions.m4 was 
missing a close quote.  OK to apply?

m4/ChangeLog:
2006-10-02  Eric Blake  <address@hidden>

        * extensions.m4 (gl_USE_SYSTEM_EXTENSIONS): Use autoconf's
        definition in autoconf 2.60+.

ChangeLog:
2006-10-02  Eric Blake  <address@hidden>

        * modules/strnlen (Depends-on): Add extensions.

Index: m4/extensions.m4
===================================================================
RCS file: /sources/gnulib/gnulib/m4/extensions.m4,v
retrieving revision 1.10
diff -u -r1.10 extensions.m4
--- m4/extensions.m4    19 Apr 2006 23:26:18 -0000      1.10
+++ m4/extensions.m4    2 Oct 2006 17:43:19 -0000
@@ -1,4 +1,5 @@
 # Enable extensions on systems that normally disable them.
+# serial 2
 
 # Copyright (C) 2003, 2006 Free Software Foundation, Inc.
 # This file is free software; the Free Software Foundation
@@ -12,6 +13,9 @@
 # ------------------------
 # Enable extensions on systems that normally disable them,
 # typically due to standards-conformance issues.
+m4_ifdef([AC_USE_SYSTEM_EXTENSIONS],
+[AC_DEFUN([gl_USE_SYSTEM_EXTENSIONS],
+  [AC_REQUIRE([AC_USE_SYSTEM_EXTENSIONS])])], [
 AC_DEFUN([gl_USE_SYSTEM_EXTENSIONS], [
   AC_BEFORE([$0], [AC_COMPILE_IFELSE])
   AC_BEFORE([$0], [AC_RUN_IFELSE])
@@ -39,4 +43,4 @@
   test $ac_cv_safe_to_define___extensions__ = yes &&
     AC_DEFINE([__EXTENSIONS__])
   AC_DEFINE([_POSIX_PTHREAD_SEMANTICS])
-])
+])])])
Index: modules/strnlen
===================================================================
RCS file: /sources/gnulib/gnulib/modules/strnlen,v
retrieving revision 1.8
diff -u -r1.8 strnlen
--- modules/strnlen     21 Aug 2006 21:46:32 -0000      1.8
+++ modules/strnlen     2 Oct 2006 17:43:19 -0000
@@ -7,6 +7,7 @@
 m4/strnlen.m4
 
 Depends-on:
+extensions
 
 configure.ac:
 gl_FUNC_STRNLEN