Small makefile change, posibility to add defines on the commandline, and fix...

Small makefile change, posibility to add defines on the commandline, and fix compiling with watchdog enabled when using the Makefile.

Marlin/Makefile

@@ -190,7 +190,8 @@ SRC = wiring.c \
 CXXSRC = WMath.cpp WString.cpp Print.cpp Marlin_main.cpp	\
 	MarlinSerial.cpp Sd2Card.cpp SdBaseFile.cpp SdFatUtil.cpp	\
 	SdFile.cpp SdVolume.cpp motion_control.cpp planner.cpp		\
-	stepper.cpp temperature.cpp cardreader.cpp ConfigurationStore.cpp
+	stepper.cpp temperature.cpp cardreader.cpp ConfigurationStore.cpp \
+	watchdog.cpp
 CXXSRC += LiquidCrystal.cpp ultralcd.cpp SPI.cpp
 
 #Check for Arduino 1.0.0 or higher and use the correct sourcefiles for that version
@@ -212,9 +213,11 @@ DEBUG = stabs
 
 OPT = s
 
+DEFINES ?=
+
 # Place -D or -U options here
-CDEFS = -DF_CPU=$(F_CPU)
-CXXDEFS = -DF_CPU=$(F_CPU)
+CDEFS = -DF_CPU=$(F_CPU) ${addprefix -D , $(DEFINES)}
+CXXDEFS = -DF_CPU=$(F_CPU) ${addprefix -D , $(DEFINES)}
 
 # Add all the source directories as include directories too
 CINCS = ${addprefix -I ,${VPATH}}