better V=1 makefile output

Makefile

@@ -18,6 +18,7 @@
 # be silent per default, but 'make V=1' will show all compiler calls.
 ifneq ($(V),1)
 Q := @
+NULL := 2> /dev/null
 endif
 
 # the final binary name (without extension)
@@ -146,13 +147,13 @@ $(LIB_DIR)/lib$(LIBNAME).a:
 
 bootloader: $(BOOTLOADER)
 	$(info flashing USB DFU bootloader $(<))
-	$(Q)$(OOCD) --file interface/$(OOCD_INTERFACE).cfg --file target/$(OOCD_TARGET).cfg --command "init" --command "reset init" --command "flash write_image erase $(<) 0x08000000" --command "reset" --command "shutdown" 2> /dev/null
+	$(Q)$(OOCD) --file interface/$(OOCD_INTERFACE).cfg --file target/$(OOCD_TARGET).cfg --command "init" --command "reset init" --command "flash write_image erase $(<) 0x08000000" --command "reset" --command "shutdown" $(NULL)
 
 flash: flash-swd
 
 flash-swd: $(BINARY).hex
 	$(info flashing $(<) using SWD)
-	$(Q)$(OOCD) --file interface/$(OOCD_INTERFACE).cfg --file target/$(OOCD_TARGET).cfg --command "init" --command "reset init" --command "flash write_image erase $(<)" --command "reset" --command "shutdown" 2> /dev/null
+	$(Q)$(OOCD) --file interface/$(OOCD_INTERFACE).cfg --file target/$(OOCD_TARGET).cfg --command "init" --command "reset init" --command "flash write_image erase $(<)" --command "reset" --command "shutdown" $(NULL)
 
 flash-dfu: $(BINARY).bin
 	$(info flashing $(<) using DFU)