Fix dependencies for godot-cpp bindings

Use an order-only prerequisite on api.json to prevent make from
re-running scons for the godot-cpp bindings

Makefile

@@ -188,7 +188,11 @@ API_CLASSES+= $(__GODOT_CPP_GEN_CLASSES)
 GODOT_CPP_GEN_CPP=$(API_CLASSES:%=godot-cpp/src/gen/%.cpp)
 GODOT_CPP_GEN_OBJS=$(API_CLASSES:%=godot-cpp/src/gen/%.o)
 # reset -I fixes the terminal which gets bunged up by this step...
-$(GODOT_CPP_GEN_CPP) $(GODOT_CPP_OBJS) $(GODOT_CPP_GEN_DIR)&: $(GODOT_CPP_API_JSON)
+# api.json is an order only prerequisite because the scons script doesn't take it's date
+# into account when generating these artifacts which causes make to re-run it for each one when they
+# don't get updated to a newer date than api.json
+# You will have to clean the submodule to re-build these artifacts.
+$(GODOT_CPP_GEN_CPP) $(GODOT_CPP_OBJS) $(GODOT_CPP_GEN_DIR)&: | $(GODOT_CPP_API_JSON)
 	cd godot-cpp; set -e; \
 	scons generate_bindings=yes platform=$(PLATFORM) use_mingw=yes -j$$(nproc) > /dev/null || (echo 'SCONS FAIL'; false)