screen: Include termios for NetBSD

Otherwise it won't build.

src/screen.cpp

@@ -10,6 +10,7 @@
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <termios.h>
 #include <time.h>
 #include <unistd.h>
 #include <cstring>