adds a utility to dump the gdt, adds serial printing for printf in testing

libc/stdio/putchar.c

@@ -2,12 +2,18 @@
 
 #if defined(__is_libk)
 #include <kernel/tty.h>
+#ifdef __TESTING__
+#include <kernel/serial.h>
+#endif
 #endif
 
 int putchar(int ic) {
 #if defined(__is_libk)
 	char c = (char) ic;
 	terminal_write(&c, sizeof(c));
+#ifdef __TESTING__
+	serial_write(&c, sizeof(c));
+#endif
 #else
 	// TODO: Implement stdio and the write system call.
 #endif