Ensure cpu_demo and tty_demo build for make test

Makefile

@@ -95,6 +95,12 @@ vector_add.exe: code/vector_add.c
 plt_example.exe: code/plt_example.c
 	gcc -fPIC -no-pie -o $@ $<
 
+cpu_demo.exe: code/cpu_demo.c
+	gcc -o $@ $<
+
+tty_demo.exe: code/tty_demo.c
+	gcc -o $@ $<
+
 speed_demo_%.exe: code/speed_demo/%/main.exe
 	cp $< $@