maint: update to latest gnulib

Required for the copyright year bump to keep 'make syntax-check'
happy, and also pulls in several portability fixes.

* .gnulib: Update to latest.
* bootstrap: Resync from upstream.
* gnulib/local/m4/ssize_t.m4.diff: Regenerate.
Signed-off-by: NEric Blake <eblake@redhat.com>

.gnulib @ 6cc32c63

-Subproject commit f39477dba778e99392948dd3dd19ec0d46aee932
+Subproject commit 6cc32c63e80bc1a30c521b2f07f2b54909b59892

bootstrap

@@ -4,7 +4,7 @@ scriptversion=2014-12-08.12; # UTC
 
 # Bootstrap this package from checked-out sources.
 
-# Copyright (C) 2003-2015 Free Software Foundation, Inc.
+# Copyright (C) 2003-2016 Free Software Foundation, Inc.
 
 # 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

gnulib/local/m4/ssize_t.m4.diff

@@ -5,7 +5,7 @@ index 209d64c..5ea72a1 100644
 @@ -1,4 +1,4 @@
 -# ssize_t.m4 serial 5 (gettext-0.18.2)
 +# ssize_t.m4 serial 6 (gettext-0.18.2)
- dnl Copyright (C) 2001-2003, 2006, 2010-2015 Free Software Foundation, Inc.
+ dnl Copyright (C) 2001-2003, 2006, 2010-2016 Free Software Foundation, Inc.
  dnl This file is free software; the Free Software Foundation
  dnl gives unlimited permission to copy and/or distribute it,
 @@ -17,7 +17,21 @@ AC_DEFUN([gt_TYPE_SSIZE_T],