Update configure.ac and a few macros used by it

The changes done to configure.ac are essentially divided in two categories:
the first is made of changes to improve existing checks, even if it's merely
in the message being printed during the check; the second category is made of
updates aimed at bringing this file closer to Autoconf 2.71, which deprecated
or even removed some stuff that was otherwise present either directly in
configure.ac or in one of the macros it includes, which have been updated in
this commit too.

Actually, the generated configure script was created by Autoconf 2.71 during
deveopment, so in a way it's already compatible with the latest version.

1 files changed, 7 insertions, 14 deletions

diff --git a/m4/libunistring.m4 b/m4/libunistring.m4
index c1bf4d553..e3d944793 100644
--- a/m4/libunistring.m4
+++ b/m4/libunistring.m4
@@ -1,9 +1,11 @@
-# libunistring.m4 serial 11
-dnl Copyright (C) 2009-2012 Free Software Foundation, Inc.
+# libunistring.m4 serial 12
+dnl Copyright (C) 2009-2021 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
 dnl with or without modifications, as long as this notice is preserved.
 
+AC_PREREQ([2.64])
+
 dnl gl_LIBUNISTRING
 dnl Searches for an installed libunistring.
 dnl If found, it sets and AC_SUBSTs HAVE_LIBUNISTRING=yes and the LIBUNISTRING
@@ -12,8 +14,8 @@ dnl augments the CPPFLAGS variable, and #defines HAVE_LIBUNISTRING to 1.
 dnl Otherwise, it sets and AC_SUBSTs HAVE_LIBUNISTRING=no and LIBUNISTRING and
 dnl LTLIBUNISTRING to empty.
 
-dnl Define gl_LIBUNISTRING using AC_DEFUN_ONCE for Autoconf >= 2.64, in order
-dnl to avoid warnings like
+dnl Define gl_LIBUNISTRING using AC_DEFUN_ONCE, in order dnl to avoid warnings
+dnl like
 dnl "warning: AC_REQUIRE: `gl_LIBUNISTRING' was expanded before it was required".
 dnl This is tricky because of the way 'aclocal' is implemented:
 dnl - It requires defining an auxiliary macro whose name ends in AC_DEFUN.
@@ -21,16 +23,7 @@ dnl   Otherwise aclocal's initial scan pass would miss the macro definition.
 dnl - It requires a line break inside the AC_DEFUN_ONCE and AC_DEFUN expansions.
 dnl   Otherwise aclocal would emit many "Use of uninitialized value $1"
 dnl   warnings.
-m4_define([gl_libunistring_AC_DEFUN],
-  m4_version_prereq([2.64],
-    [[AC_DEFUN_ONCE(
-        [$1], [$2])]],
-    [m4_ifdef([gl_00GNULIB],
-       [[AC_DEFUN_ONCE(
-           [$1], [$2])]],
-       [[AC_DEFUN(
-           [$1], [$2])]])]))
-gl_libunistring_AC_DEFUN([gl_LIBUNISTRING],
+AC_DEFUN_ONCE([gl_LIBUNISTRING],
 [
   AC_BEFORE([$0], [gl_LIBUNISTRING_MODULE])
   AC_BEFORE([$0], [gl_LIBUNISTRING_LIBHEADER])