For some systems vsnprintf() exists in the system libraries but not in the
headers, so we need to declare it ourselves to be able to use it.
*/
-#ifndef HAVE_VSNPRINTF_DECL
+#if defined(HAVE_VSNPRINTF) && !defined(HAVE_VSNPRINTF_DECL)
extern "C"
int vsnprintf(char *str, size_t size, const char *format, va_list ap);
#endif // !HAVE_VSNPRINTF_DECL