Rework the vboot_reference make system.

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 CXX ?= g++
 export CFLAGS = -Wall -DNDEBUG -O3 -Werror
 export TOP = $(shell pwd)
 export FWDIR=$(TOP)/vboot_firmware
 export HOSTDIR=$(TOP)/host
 export INCLUDES = \
         -I$(FWDIR)/include \
         -I$(TOP)/misclibs/include
 
-export FWLIB=$(FWDIR)/vboot_fw.a
-export HOSTLIB=$(HOSTDIR)/vboot_host.a
+export BUILD = ${TOP}/build
+export FWLIB = ${BUILD}/vboot_fw.a
+export HOSTLIB= ${BUILD}/vboot_host.a
 
-SUBDIRS=vboot_firmware misclibs host vfirmware vkernel utility cgpt tests
+SUBDIRS = vboot_firmware misclibs host vfirmware vkernel utility cgpt tests
 
 all:
         set -e; \
+        for d in $(shell find ${SUBDIRS} -name '*.c' -exec  dirname {} \; |\
+                 sort -u); do \
+                newdir=${BUILD}/$$d; \
+                if [ ! -d $$newdir ]; then \
+                        mkdir -p $$newdir; \
+                fi; \
+        done && \
         for i in $(SUBDIRS); do \
                 make -C $$i; \
         done
 
 clean:
-        set -e; \
-        for i in $(SUBDIRS); do \
-                make -C $$i clean; \
-        done
+        /bin/rm -rf ${BUILD}
 
 install:
         $(MAKE) -C utility install
         $(MAKE) -C cgpt install
 
 runtests:
         $(MAKE) -C tests runtests