Update gnulib

This updates gnulib to a relatively recent commit.  Most of this was
done by the gnulib import script; the only change I made was to
update-gnulib.sh.

Tested on x86-64 Fedora 34.  I also did a mingw cross build.

gnulib/import/m4/vararrays.m4

@@ -0,0 +1,72 @@
+# Check for variable-length arrays.
+
+# serial 6
+
+# From Paul Eggert
+
+# Copyright (C) 2001, 2009-2022 Free Software Foundation, Inc.
+# This file is free software; the Free Software Foundation
+# gives unlimited permission to copy and/or distribute it,
+# with or without modifications, as long as this notice is preserved.
+
+m4_version_prereq([2.70], [], [
+
+# AC_C_VARARRAYS
+# --------------
+# Check whether the C compiler supports variable-length arrays.
+AC_DEFUN([AC_C_VARARRAYS],
+[
+  AC_CACHE_CHECK([for variable-length arrays],
+    ac_cv_c_vararrays,
+    [AC_EGREP_CPP([defined],
+       [#ifdef __STDC_NO_VLA__
+        defined
+        #endif
+       ],
+       [ac_cv_c_vararrays='no: __STDC_NO_VLA__ is defined'],
+       [AC_COMPILE_IFELSE(
+          [AC_LANG_PROGRAM(
+             [[/* Test for VLA support.  This test is partly inspired
+                  from examples in the C standard.  Use at least two VLA
+                  functions to detect the GCC 3.4.3 bug described in:
+                  https://lists.gnu.org/archive/html/bug-gnulib/2014-08/msg00014.html
+                  */
+               #ifdef __STDC_NO_VLA__
+                syntax error;
+               #else
+                 extern int n;
+                 int B[100];
+                 int fvla (int m, int C[m][m]);
+
+                 int
+                 simple (int count, int all[static count])
+                 {
+                   return all[count - 1];
+                 }
+
+                 int
+                 fvla (int m, int C[m][m])
+                 {
+                   typedef int VLA[m][m];
+                   VLA x;
+                   int D[m];
+                   static int (*q)[m] = &B;
+                   int (*s)[n] = q;
+                   return C && &x[0][0] == &D[0] && &D[0] == s[0];
+                 }
+               #endif
+               ]])],
+          [ac_cv_c_vararrays=yes],
+          [ac_cv_c_vararrays=no])])])
+  if test "$ac_cv_c_vararrays" = yes; then
+    dnl This is for compatibility with Autoconf 2.61-2.69.
+    AC_DEFINE([HAVE_C_VARARRAYS], 1,
+      [Define to 1 if C supports variable-length arrays.])
+  elif test "$ac_cv_c_vararrays" = no; then
+    AC_DEFINE([__STDC_NO_VLA__], 1,
+      [Define to 1 if C does not support variable-length arrays, and
+       if the compiler does not already define this.])
+  fi
+])
+
+])