vfscanf-internal: Remove potentially unbounded allocas

Some locales define a list of mapping pairs of alternate digits and
separators for input digits (to_inpunct).  This require the scanf
to create a list of all possible inputs for the optional type
modifier 'I'.

Checked on x86_64-linux-gnu.

Reviewed-by: Joe Simmons-Talbott <josimmon@redhat.com>

stdio-common/tst-scanf-to_inpunct.c

@@ -0,0 +1,78 @@
+/* Test scanf for languages with mapping pairs of alternate digits and
+   separators.
+   Copyright (C) 2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library 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
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <array_length.h>
+#include <stdio.h>
+#include <support/support.h>
+#include <support/check.h>
+
+/* fa_IR defines to_inpunct for numbers.  */
+static const struct
+{
+  int n;
+  const char *str;
+} inputs[] =
+{
+  { 1,    "\xdb\xb1" },
+  { 2,    "\xdb\xb2" },
+  { 3,    "\xdb\xb3" },
+  { 4,    "\xdb\xb4" },
+  { 5,    "\xdb\xb5" },
+  { 6,    "\xdb\xb6" },
+  { 7,    "\xdb\xb7" },
+  { 8,    "\xdb\xb8" },
+  { 9,    "\xdb\xb9" },
+  { 10,   "\xdb\xb1\xdb\xb0" },
+  { 11,   "\xdb\xb1\xdb\xb1" },
+  { 12,   "\xdb\xb1\xdb\xb2" },
+  { 13,   "\xdb\xb1\xdb\xb3" },
+  { 14,   "\xdb\xb1\xdb\xb4" },
+  { 15,   "\xdb\xb1\xdb\xb5" },
+  { 16,   "\xdb\xb1\xdb\xb6" },
+  { 17,   "\xdb\xb1\xdb\xb7" },
+  { 18,   "\xdb\xb1\xdb\xb8" },
+  { 19,   "\xdb\xb1\xdb\xb9" },
+  { 20,   "\xdb\xb2\xdb\xb0" },
+  { 30,   "\xdb\xb3\xdb\xb0" },
+  { 40,   "\xdb\xb4\xdb\xb0" },
+  { 50,   "\xdb\xb5\xdb\xb0" },
+  { 60,   "\xdb\xb6\xdb\xb0" },
+  { 70,   "\xdb\xb7\xdb\xb0" },
+  { 80,   "\xdb\xb8\xdb\xb0" },
+  { 90,   "\xdb\xb9\xdb\xb0" },
+  { 100,  "\xdb\xb1\xdb\xb0\xdb\xb0" },
+  { 1000, "\xdb\xb1\xdb\xb0\xdb\xb0\xdb\xb0" },
+};
+
+static int
+do_test (void)
+{
+  xsetlocale (LC_ALL, "fa_IR.UTF-8");
+
+  for (int i = 0; i < array_length (inputs); i++)
+    {
+      int n;
+      sscanf (inputs[i].str, "%Id", &n);
+      TEST_COMPARE (n, inputs[i].n);
+    }
+
+  return 0;
+}
+
+#include <support/test-driver.c>