stdio-common: Add tests for formatted sprintf output specifiers

Wire sprintf into test infrastructure for formatted printf output
specifiers.

Reviewed-by: DJ Delorie <dj@redhat.com>

stdio-common/tst-printf-format-s.h

@@ -0,0 +1,60 @@
+/* Test feature wrapper for formatted 'sprintf' output.
+   Copyright (C) 2024 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 <stdio.h>
+#include <stdlib.h>
+
+#include <support/next_to_fault.h>
+
+#define SPRINTF_BUFFER_SIZE 65536
+
+static struct support_next_to_fault ntf;
+
+#define PREPARE printf_under_test_init
+static void
+printf_under_test_init (int argc, char **argv)
+{
+  ntf = support_next_to_fault_allocate (SPRINTF_BUFFER_SIZE);
+}
+
+static void __attribute__ ((destructor))
+printf_under_test_fini (void)
+{
+  support_next_to_fault_free (&ntf);
+}
+
+#define printf_under_test(...)						\
+({									\
+  __label__ out;							\
+  char *str = ntf.buffer;						\
+  int result;								\
+									\
+  result = sprintf (str, __VA_ARGS__);					\
+  if (result < 0)							\
+    {									\
+      perror ("sprintf");						\
+      goto out;								\
+    }									\
+  if (fwrite (str, sizeof (*str), result, stdout) != result)		\
+    {									\
+      perror ("fwrite");						\
+      result = -1;							\
+    }									\
+out:									\
+  result;								\
+})