Keep temp files in the output directory.

firmware/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.
 
 FWTOP := $(shell pwd)
 LIBDIR = $(FWTOP)/lib
 STUBDIR = $(FWTOP)/stub
 TESTDIR = $(FWTOP)/linktest
 BUILD_ROOT := ${BUILD}/$(shell basename ${FWTOP})
 
@@ skipping 30 matching lines @@
 
 ALL_SRCS = ${LIB_SRCS} ${STUB_SRCS} version.c
 
 test : $(FWLIB) update-version
         $(CC) $(CFLAGS) $(INCLUDES) -o $(BUILD_ROOT)/a.out \
                 $(TESTDIR)/main.c $(FWLIB)
 
 # This is executed at every make, to see if anything has changed
 update-version :
         find \( -name '*.[ch]' -o -name 'Makefile*' \) -a \! -name version.c \
-                | sort | xargs cat | md5sum | cut -c 25-32 > x.tmp
-        echo "char* VbootVersion = \"VBOOv=$$(cat x.tmp)\";" > version.tmp
-        cmp -s version.tmp version.c || \
-                ( echo "** Updating version.c **" && \
-                  cp version.tmp version.c )
-
+                | sort | xargs cat | md5sum | cut -c 25-32 > \
+        ${BUILD_ROOT}/x.tmp && \
+        echo "char* VbootVersion = \"VBOOv=$$(cat ${BUILD_ROOT}/x.tmp)\";" > \
+                ${BUILD_ROOT}\version.tmp && \
+        (cmp -s ${BUILD_ROOT}\version.tmp version.c || \
+                ( echo "** Updating version.c **" &&  \
+                  cp ${BUILD_ROOT}\version.tmp version.c))
 
 include ../common.mk
 
 $(FWLIB) : $(ALL_OBJS)
         rm -f $@
         ar qc $@ $^