libs/libc/syslog/lib_syslog.c: Bring back the commit 2e8eba35ff 'libs/libc/syslog/lib_syslog.c: Fix syslog crash on 64bit simulation'. This has more detailed information:

https://stackoverflow.com/questions/10807310/platform-inconsistencies-with-vsprintf-and-va-list.

libs/libc/syslog/lib_syslog.c

@@ -77,7 +77,15 @@ void vsyslog(int priority, FAR const IPTR char *fmt, va_list ap)
        * of structures in the NuttX syscalls does not work.
        */
 
-      (void)nx_vsyslog(priority, fmt, &ap);
+#ifdef va_copy
+      va_list copy;
+
+      va_copy(copy, ap);
+      nx_vsyslog(priority, fmt, &copy);
+      va_end(copy);
+#else
+      nx_vsyslog(priority, fmt, &ap);
+#endif
     }
 }