Add GCC printf formatting checks

Author: MCUdude

Print.h

@@ -44,10 +44,10 @@ class Print
     void setWriteError(int err = 1) { write_error = err; }
   public:
     Print() : write_error(0) {}
-  
+
     int getWriteError() { return write_error; }
     void clearWriteError() { setWriteError(0); }
-  
+
     virtual size_t write(uint8_t) = 0;
     size_t write(const char *str) {
       if (str == NULL) return 0;
@@ -88,8 +88,8 @@ class Print
     size_t println(double, int = 2);
     size_t println(const Printable&);
     size_t println(void);
-    
-    int16_t printf(const char *format, ...);
+
+    int16_t printf(const char *format, ...) __attribute__ ((format (printf, 2, 3)));
     int16_t printf(const __FlashStringHelper *format, ...);
 };