Fix Gen7 compile if you have avr-libc version 1.7.1 or higher. See http://code.google.com/p/arduino/issues/detail?id=604

Marlin/Gen7/cores/arduino/wiring.h

 #define max(a,b) ((a)>(b)?(a):(b))
 #define abs(x) ((x)>0?(x):-(x))
 #define constrain(amt,low,high) ((amt)<(low)?(low):((amt)>(high)?(high):(amt)))
+#if __AVR_LIBC_VERSION__ < 10701UL
 #define round(x)     ((x)>=0?(long)((x)+0.5):(long)((x)-0.5))
+#endif
 #define radians(deg) ((deg)*DEG_TO_RAD)
 #define degrees(rad) ((rad)*RAD_TO_DEG)
 #define sq(x) ((x)*(x))