Merge pull request #554 from iXce/cxa_atexit

Fix Makefile-based build when avr-gcc has been compiled with --enable-cxa_atexit

Marlin/Makefile

 CTUNING += -DMOTHERBOARD=${HARDWARE_MOTHERBOARD}
 endif
 #CEXTRA = -Wa,-adhlns=$(<:.c=.lst)
+CEXTRA = -fno-use-cxa-atexit
 
 CFLAGS := $(CDEBUG) $(CDEFS) $(CINCS) -O$(OPT) $(CWARN) $(CEXTRA) $(CTUNING)
 CXXFLAGS :=         $(CDEFS) $(CINCS) -O$(OPT) -Wall    $(CEXTRA) $(CTUNING)