Add stpeprintf()

[v]stpeprintf() are similar to [v]snprintf(3), but they allow chaining.
[v]snprintf(3) are very dangerous for catenating strings, since the
obvious ways to do it invoke Undefined Behavior, and the ways that avoid
UB are very error-prone.

Cc: Iker Pedrosa <ipedrosa@redhat.com>
Signed-off-by: Alejandro Colomar <alx@kernel.org>

libmisc/stpeprintf.c

@@ -0,0 +1,25 @@
+/*
+ * SPDX-FileCopyrightText:  2022 - 2023, Alejandro Colomar <alx@kernel.org>
+ *
+ * SPDX-License-Identifier:  BSD-3-Clause
+ */
+
+
+#include <config.h>
+
+#if !defined(HAVE_STPEPRINTF)
+
+#ident "$Id$"
+
+#include "stpeprintf.h"
+
+#include <stdarg.h>
+
+
+extern inline char *stpeprintf(char *dst, char *end, const char *restrict fmt,
+    ...);
+extern inline char *vstpeprintf(char *dst, char *end, const char *restrict fmt,
+    va_list ap);
+
+
+#endif  // !HAVE_STPEPRINTF