feat(uart): eliminates nonexistent functions (espressif#10428)

loop() calls Serial Events functions when those are declared. The way it was declared was forcing to alway call avalable() to then call an empty function. This commit fixes it.

Author: SuGlider

cores/esp32/HardwareSerial.cpp

@@ -24,16 +24,13 @@
 #endif
 
 void serialEvent(void) __attribute__((weak));
-void serialEvent(void) {}
 
 #if SOC_UART_NUM > 1
 void serialEvent1(void) __attribute__((weak));
-void serialEvent1(void) {}
 #endif /* SOC_UART_NUM > 1 */
 
 #if SOC_UART_NUM > 2
 void serialEvent2(void) __attribute__((weak));
-void serialEvent2(void) {}
 #endif /* SOC_UART_NUM > 2 */
 
 #if !defined(NO_GLOBAL_INSTANCES) && !defined(NO_GLOBAL_SERIAL)
@@ -48,37 +45,35 @@ HardwareSerial Serial2(2);
 
 #if HWCDC_SERIAL_IS_DEFINED == 1  // Hardware JTAG CDC Event
 extern void HWCDCSerialEvent(void) __attribute__((weak));
-void HWCDCSerialEvent(void) {}
 #endif
 
 #if USB_SERIAL_IS_DEFINED == 1  // Native USB CDC Event
 // Used by Hardware Serial for USB CDC events
 extern void USBSerialEvent(void) __attribute__((weak));
-void USBSerialEvent(void) {}
 #endif
 
 void serialEventRun(void) {
 #if HWCDC_SERIAL_IS_DEFINED == 1  // Hardware JTAG CDC Event
-  if (HWCDCSerial.available()) {
+  if (HWCDCSerialEvent && HWCDCSerial.available()) {
     HWCDCSerialEvent();
   }
 #endif
 #if USB_SERIAL_IS_DEFINED == 1  // Native USB CDC Event
-  if (USBSerial.available()) {
+  if (USBSerialEvent && USBSerial.available()) {
     USBSerialEvent();
   }
 #endif
   // UART0 is default serialEvent()
-  if (Serial0.available()) {
+  if (serialEvent && Serial0.available()) {
     serialEvent();
   }
 #if SOC_UART_NUM > 1
-  if (Serial1.available()) {
+  if (serialEvent1 && Serial1.available()) {
     serialEvent1();
   }
 #endif
 #if SOC_UART_NUM > 2
-  if (Serial2.available()) {
+  if (serialEvent2 && Serial2.available()) {
     serialEvent2();
   }
 #endif