simulation: add warnings to firmware makefile

Signed-off-by: Manohar Vanga <manohar.vanga@cern.ch>

simulation/fw/Makefile

-CFLAGS += -I../include
+CFLAGS += -I../include -Wall -Wextra
 
 all: wb_cfggen
 
 wb_cfggen: wb_cfggen.o
-	gcc wb_cfggen.o -o wb_cfggen
+	$(CC) $(CFLAGS) wb_cfggen.o -o wb_cfggen
 
 clean:
 	rm -rf wb_cfggen *.o