firmware: fix builds with gcc stack smashing protection enabled

On Ubuntu 20.04 when builiding dpkg packages, even when cross-compiling
firmware, gcc stack smashing protection is enabled.  Let's provide what
is minimally required in order to sucessfully complete builds on such
platforms.

Change-Id: Ic2f68f16b0730e7b5db17c30effc29a2909d1997
Closes: OS#4687
diff --git a/firmware/Makefile b/firmware/Makefile
index bdca6e5..7be5c30 100644
--- a/firmware/Makefile
+++ b/firmware/Makefile
@@ -100,7 +100,7 @@
 C_LIBUSB_RT  = dfu.c dfu_runtime.c
 C_LIBUSB_DFU = dfu.c dfu_desc.c dfu_driver.c
 C_LIBCOMMON  = string.c stdio.c fputs.c usb_buf.c ringbuffer.c pseudo_talloc.c host_communication.c \
-	       main_common.c
+	       main_common.c stack_check.c
 
 C_BOARD      = $(notdir $(wildcard libboard/common/source/*.c))
 C_BOARD     += $(notdir $(wildcard libboard/$(BOARD)/source/*.c))