iconv.m4: avoid warning

[Bruno Haible]

Somehow I got this autoconf warning:

  configure.ac:127: warning: AC_REQUIRE: `AM_ICONV' was expanded before it was 
required

AM_ICONV is AC_REQUIREd in many places, but documented as an invokable macro in
the gettext documentation. Therefore it makes sense to use AC_DEFUN_ONCE. I'm
applying this:


2010-05-16  Bruno Haible  <address@hidden>

        Avoid autoconf warnings about AM_ICONV.
        * m4/iconv.m4 (AM_ICONV): Define using AM_DEFUN_ONCE for autoconf >=
        2.64.

--- m4/iconv.m4.orig    Sun May 16 23:46:09 2010
+++ m4/iconv.m4 Sun May 16 23:45:56 2010
@@ -1,4 +1,4 @@
-# iconv.m4 serial 9 (gettext-0.18)
+# iconv.m4 serial 10 (gettext-0.18.1)
 dnl Copyright (C) 2000-2002, 2007-2010 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -170,7 +170,10 @@
   AC_SUBST([LTLIBICONV])
 ])
 
-AC_DEFUN([AM_ICONV],
+dnl Define AM_ICONV using AC_DEFUN_ONCE for Autoconf >= 2.64, in order to
+dnl avoid warnings like
+dnl "warning: AC_REQUIRE: `AM_ICONV' was expanded before it was required".
+m4_version_prereq([2.64],[AC_DEFUN_ONCE],[AC_DEFUN])([AM_ICONV],
 [
   AM_ICONV_LINK
   if test "$am_cv_func_iconv" = yes; then