Fix incorrect %zd formatting directives

%zd is for ssize_t. For size_t we should use %zu.

backend/headless/output.c

@@ -118,12 +118,12 @@ struct wlr_output *wlr_headless_add_output(struct wlr_backend *wlr_backend,
 	strncpy(wlr_output->model, "headless", sizeof(wlr_output->model));
 
 	char name[64];
-	snprintf(name, sizeof(name), "HEADLESS-%zd", ++backend->last_output_num);
+	snprintf(name, sizeof(name), "HEADLESS-%zu", ++backend->last_output_num);
 	wlr_output_set_name(wlr_output, name);
 
 	char description[128];
 	snprintf(description, sizeof(description),
-		"Headless output %zd", backend->last_output_num);
+		"Headless output %zu", backend->last_output_num);
 	wlr_output_set_description(wlr_output, description);
 
 	struct wl_event_loop *ev = wl_display_get_event_loop(backend->display);

backend/wayland/output.c

@@ -522,12 +522,12 @@ struct wlr_output *wlr_wl_output_create(struct wlr_backend *wlr_backend) {
 	strncpy(wlr_output->model, "wayland", sizeof(wlr_output->model));
 
 	char name[64];
-	snprintf(name, sizeof(name), "WL-%zd", ++backend->last_output_num);
+	snprintf(name, sizeof(name), "WL-%zu", ++backend->last_output_num);
 	wlr_output_set_name(wlr_output, name);
 
 	char description[128];
 	snprintf(description, sizeof(description),
-		"Wayland output %zd", backend->last_output_num);
+		"Wayland output %zu", backend->last_output_num);
 	wlr_output_set_description(wlr_output, description);
 
 	output->backend = backend;

backend/x11/output.c

@@ -513,14 +513,14 @@ struct wlr_output *wlr_x11_output_create(struct wlr_backend *backend) {
 	wlr_output_update_custom_mode(wlr_output, 1024, 768, 0);
 
 	char name[64];
-	snprintf(name, sizeof(name), "X11-%zd", ++x11->last_output_num);
+	snprintf(name, sizeof(name), "X11-%zu", ++x11->last_output_num);
 	wlr_output_set_name(wlr_output, name);
 
 	parse_xcb_setup(wlr_output, x11->xcb);
 
 	char description[128];
 	snprintf(description, sizeof(description),
-		"X11 output %zd", x11->last_output_num);
+		"X11 output %zu", x11->last_output_num);
 	wlr_output_set_description(wlr_output, description);
 
 	// The X11 protocol requires us to set a colormap and border pixel if the