Make SPI interrupt handlers weak and fix example ambiguity

- Add __attribute__((weak)) to all SPI interrupt handlers (SERCOM4, SPI1, etc)
  This allows variants to override them when SERCOM is used for other
  peripherals (e.g., MKR variants use SERCOM4 for Serial2/UART)

- Explicitly cast slave addresses to uint8_t in Wire examples to avoid
  any potential overload resolution issues on different compiler versions

Author: crabel99

libraries/SPI/SPI.cpp

@@ -364,6 +364,7 @@ void SPIClass::detachInterrupt() {
   #ifndef SPI_IT_HANDLER
     #define SPI_IT_HANDLER      SERCOM4_Handler
   #endif
+  void SPI_IT_HANDLER(void) __attribute__ ((weak));
   void SPI_IT_HANDLER(void) { SPI.onService(); }
 
   #if defined(__SAMD51__)
@@ -373,6 +374,10 @@ void SPIClass::detachInterrupt() {
       #define SPI_IT_HANDLER_2 SERCOM4_2_Handler
       #define SPI_IT_HANDLER_3 SERCOM4_3_Handler
     #endif
+    void SPI_IT_HANDLER_0(void) __attribute__ ((weak));
+    void SPI_IT_HANDLER_1(void) __attribute__ ((weak));
+    void SPI_IT_HANDLER_2(void) __attribute__ ((weak));
+    void SPI_IT_HANDLER_3(void) __attribute__ ((weak));
     void SPI_IT_HANDLER_0(void) { SPI.onService(); }
     void SPI_IT_HANDLER_1(void) { SPI.onService(); }
     void SPI_IT_HANDLER_2(void) { SPI.onService(); }
@@ -383,10 +388,15 @@ void SPIClass::detachInterrupt() {
   SPIClass SPI1(&PERIPH_SPI1, PIN_SPI1_MISO, PIN_SPI1_SCK, PIN_SPI1_MOSI, PAD_SPI1_TX, PAD_SPI1_RX);
 
   #if defined(SPI1_IT_HANDLER)
+    void SPI1_IT_HANDLER(void) __attribute__ ((weak));
     void SPI1_IT_HANDLER(void) { SPI1.onService(); }
   #endif
 
   #if defined(__SAMD51__) && defined(SPI1_IT_HANDLER_0)
+    void SPI1_IT_HANDLER_0(void) __attribute__ ((weak));
+    void SPI1_IT_HANDLER_1(void) __attribute__ ((weak));
+    void SPI1_IT_HANDLER_2(void) __attribute__ ((weak));
+    void SPI1_IT_HANDLER_3(void) __attribute__ ((weak));
     void SPI1_IT_HANDLER_0(void) { SPI1.onService(); }
     void SPI1_IT_HANDLER_1(void) { SPI1.onService(); }
     void SPI1_IT_HANDLER_2(void) { SPI1.onService(); }

libraries/Wire/examples/slave_receiver/slave_receiver.ino

@@ -14,7 +14,7 @@
 
 void setup()
 {
-  Wire.begin(4);                // join i2c bus with address #4
+  Wire.begin((uint8_t)4);       // join i2c bus with address #4
   Wire.onReceive(receiveEvent); // register event
   Serial.begin(9600);           // start serial for output
 }

libraries/Wire/examples/slave_sender/slave_sender.ino

@@ -14,7 +14,7 @@
 
 void setup()
 {
-  Wire.begin(2);                // join i2c bus with address #2
+  Wire.begin((uint8_t)2);       // join i2c bus with address #2
   Wire.onRequest(requestEvent); // register event
 }