util/spkmodem_recv: Use pledge but only on OpenBSD

It will only be used on OpenBSD. Other operating
systems will behave in the same way.

Pledge is feature specific to OpenBSD that
restricts system operations, for security:

https://man.openbsd.org/pledge.2

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/spkmodem_recv/spkmodem-recv.c

@@ -36,6 +36,11 @@ main(int argc, char *argv[])
 {
 	int c;
 
+#ifdef HAVE_PLEDGE
+	if (pledge("stdio", NULL) == -1)
+		err(errno, "pledge");
+#endif
+
 	while ((c = getopt(argc, argv, "u")) != -1) {
 		switch (c) {
 		case 'u':