chore: Fix builtin LED defs

Author: franky47

examples/AltPinSerial/AltPinSerial.ino

@@ -18,6 +18,11 @@
    MIDI_NAMESPACE::MidiInterface<Transport> MIDI((Transport&)serialMIDI);
 #endif
 
+// Some boards don't have this set (ESP32)
+#ifndef LED_BUILTIN
+#define LED_BUILTIN 0
+#endif
+
 void setup()
 {
   pinMode(LED_BUILTIN, OUTPUT);

examples/CustomBaudRate/CustomBaudRate.ino

@@ -15,6 +15,11 @@ struct CustomBaudRateSettings : public MIDI_NAMESPACE::DefaultSerialSettings {
     MIDI_NAMESPACE::MidiInterface<MIDI_NAMESPACE::SerialMIDI<HardwareSerial, CustomBaudRateSettings>> MIDI((MIDI_NAMESPACE::SerialMIDI<HardwareSerial, CustomBaudRateSettings>&)serialMIDI);
 #endif
 
+// Some boards don't have this set (ESP32)
+#ifndef LED_BUILTIN
+#define LED_BUILTIN 0
+#endif
+
 void setup() {
   pinMode(LED_BUILTIN, OUTPUT);
   MIDI.begin(MIDI_CHANNEL_OMNI);

examples/ErrorCallback/ErrorCallback.ino

@@ -5,6 +5,11 @@
 
 MIDI_CREATE_DEFAULT_INSTANCE();
 
+// Some boards don't have this set (ESP32)
+#ifndef LED_BUILTIN
+#define LED_BUILTIN 0
+#endif
+
 void handleError(int8_t err)
 {
   digitalWrite(LED_BUILTIN, (err == 0)? LOW : HIGH);

examples/ReceiverActiveSensing/ReceiverActiveSensing.ino

@@ -1,6 +1,11 @@
 #include <MIDI.h>
 USING_NAMESPACE_MIDI
 
+// Some boards don't have this set (ESP32)
+#ifndef LED_BUILTIN
+#define LED_BUILTIN 0
+#endif
+
 struct MyMIDISettings : public MIDI_NAMESPACE::DefaultSettings
 {
   // When setting UseReceiverActiveSensing to true, MIDI.read() *must* be called