Vboot Reference: Make length types explicitly sized.

src/platform/vboot_reference/Makefile

 # Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 export CC ?= gcc
-export CFLAGS = -Wall -ansi -DNDEBUG -O3
+export CFLAGS = -Wall -DNDEBUG -O3 -Werror
 export TOP = $(shell pwd)
 export INCLUDEDIR = $(TOP)/include
 export INCLUDES = -I$(INCLUDEDIR)
 
 SUBDIRS=common crypto utils tests
 
 all:
         for i in $(SUBDIRS); do \
         ( cd $$i ; $(MAKE)) ; \
         done
 
 clean:
         for i in $(SUBDIRS); do \
         ( cd $$i ; make clean) ; \
         done