Fix unused warning

Author: matsujirushi

cores/arduino/Retarget.cpp

@@ -53,6 +53,8 @@ int _getpid(void) {}
 extern int __real__write (int fd, const char *ptr, int len);
 
 int __wrap__write (int fd, const char *ptr, int len) {
+	(void)fd;	// UNUSED
+
 	int i;
 
 	if (!Serial) {

cores/arduino/SERCOM.h

@@ -245,7 +245,7 @@ class SERCOM
 		uint32_t getFreqRef(void) { return freqRef; };
 #else
 		// The equivalent SAMD21 dummy functions...
-		void setClockSource(int8_t idx, SercomClockSource src, bool core) {idx = 0; src = SERCOM_CLOCK_SOURCE_FCPU; core = false; };
+		void setClockSource(int8_t idx, SercomClockSource src, bool core) { (void)idx; (void)src; (void)core; };
 		SercomClockSource getClockSource(void) { return SERCOM_CLOCK_SOURCE_FCPU; };
 		uint32_t getFreqRef(void) { return F_CPU; };
 #endif