Autotools: add AX_TYPE_SOCKLEN_T m4 snippet

The AX_TYPE_SOCKLEN_T is not installed per default on many systems, so
include it in the source. This fixes a configure warning:

  `./configure: line 7752: AX_TYPE_SOCKLEN_T: command not found`

...and also makes sure the socklen_t check is actually done when
configuring.

Signed-off-by: Bert van Hall <[email protected]>

m4/ax_type_socklen_t.m4

@@ -0,0 +1,61 @@
+# ===========================================================================
+#     http://www.gnu.org/software/autoconf-archive/ax_type_socklen_t.html
+# ===========================================================================
+#
+# SYNOPSIS
+#
+#   AX_TYPE_SOCKLEN_T
+#
+# DESCRIPTION
+#
+#   Check whether sys/socket.h defines type socklen_t. Please note that some
+#   systems require sys/types.h to be included before sys/socket.h can be
+#   compiled.
+#
+# LICENSE
+#
+#   Copyright (c) 2008 Lars Brinkhoff <[email protected]>
+#
+#   This program is free software; you can redistribute it and/or modify it
+#   under the terms of the GNU General Public License as published by the
+#   Free Software Foundation; either version 2 of the License, or (at your
+#   option) any later version.
+#
+#   This program is distributed in the hope that it will be useful, but
+#   WITHOUT ANY WARRANTY; without even the implied warranty of
+#   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
+#   Public License for more details.
+#
+#   You should have received a copy of the GNU General Public License along
+#   with this program. If not, see <http://www.gnu.org/licenses/>.
+#
+#   As a special exception, the respective Autoconf Macro's copyright owner
+#   gives unlimited permission to copy, distribute and modify the configure
+#   scripts that are the output of Autoconf when processing the Macro. You
+#   need not follow the terms of the GNU General Public License when using
+#   or distributing such scripts, even though portions of the text of the
+#   Macro appear in them. The GNU General Public License (GPL) does govern
+#   all other use of the material that constitutes the Autoconf Macro.
+#
+#   This special exception to the GPL applies to versions of the Autoconf
+#   Macro released by the Autoconf Archive. When you make and distribute a
+#   modified version of the Autoconf Macro, you may extend this special
+#   exception to the GPL to apply to your modified version as well.
+
+#serial 5
+
+AU_ALIAS([TYPE_SOCKLEN_T], [AX_TYPE_SOCKLEN_T])
+AC_DEFUN([AX_TYPE_SOCKLEN_T],
+[AC_CACHE_CHECK([for socklen_t], ac_cv_ax_type_socklen_t,
+[
+  AC_TRY_COMPILE(
+  [#include <sys/types.h>
+   #include <sys/socket.h>],
+  [socklen_t len = 42; return 0;],
+  ac_cv_ax_type_socklen_t=yes,
+  ac_cv_ax_type_socklen_t=no)
+])
+  if test $ac_cv_ax_type_socklen_t != yes; then
+    AC_DEFINE(socklen_t, int, [Substitute for socklen_t])
+  fi
+])