Add default LED pin to Blink example

examples/arduino-blink/platformio.ini

@@ -40,6 +40,3 @@ platform = espressif32
 framework = arduino
 board = esp32-s3-devkitc-1
 monitor_speed = 115200
-build_flags =
-	-D LED_BUILTIN=2
-

examples/arduino-blink/src/Blink.cpp

@@ -7,7 +7,9 @@
 #include <Arduino.h>
 
 // Set LED_BUILTIN if it is not defined by Arduino framework
-// #define LED_BUILTIN 2
+#ifndef LED_BUILTIN
+    #define LED_BUILTIN 2
+#endif
 
 void setup()
 {