Let hello_double_tap run without an LED defined

Author: lurch

system/hello_double_tap/hello_double_tap.c

@@ -13,9 +13,7 @@
 // `pico_bootsel_via_double_reset` library!
 
 int main() {
-#ifndef PICO_DEFAULT_LED_PIN
-#warning system/hello_double_tap example requires a board with a regular LED
-#else
+#ifdef PICO_DEFAULT_LED_PIN
     const uint LED_PIN = PICO_DEFAULT_LED_PIN;
     gpio_init(LED_PIN);
     gpio_set_dir(LED_PIN, GPIO_OUT);
@@ -25,5 +23,9 @@ int main() {
         gpio_put(LED_PIN, 0);
         sleep_ms(250);
     }
+#else
+    while (true) {
+        sleep_ms(250);
+    }
 #endif
 }