Add support for a saving build objects in a separate directory.
Modifications are based on the linux kernel approach and
support two use cases:

  1) Add O= to the make command line
  'make O=/tmp/build all'

  2) Set environement variable BUILD_DIR to point to the desired location
  'export BUILD_DIR=/tmp/build'
  'make'

The second approach can also be used with a MAKEALL script
'export BUILD_DIR=/tmp/build'
'./MAKEALL'

Command line 'O=' setting overrides BUILD_DIR environent variable.

When none of the above methods is used the local build is performed and
the object files are placed in the source directory.
diff --git a/dtt/Makefile b/dtt/Makefile
index 0a33478..486008a 100644
--- a/dtt/Makefile
+++ b/dtt/Makefile
@@ -1,4 +1,7 @@
 #
+# (C) Copyright 2006
+# Wolfgang Denk, DENX Software Engineering, wd@denx.de.
+#
 # (C) Copyright 2001
 # Erik Theisen, Wave 7 Optics, etheisen@mindspring.com.
 #
@@ -25,20 +28,23 @@
 
 #CFLAGS += -DDEBUG
 
-LIB	= libdtt.a
+LIB	= $(obj)libdtt.a
 
-OBJS	= lm75.o ds1621.o adm1021.o
+COBJS	= lm75.o ds1621.o adm1021.o
+
+SRCS	:= $(COBJS:.o=.c)
+OBJS	:= $(addprefix $(obj),$(COBJS))
 
 all:	$(LIB)
 
-$(LIB):	$(START) $(OBJS)
+$(LIB):	$(obj).depend $(OBJS)
 	$(AR) crv $@ $(OBJS)
 
 #########################################################################
 
-.depend:	Makefile $(OBJS:.o=.c)
-		$(CC) -M $(CFLAGS) $(OBJS:.o=.c) > $@
+# defines $(obj).depend target
+include $(SRCTREE)/rules.mk
 
-sinclude .depend
+sinclude $(obj).depend
 
 #########################################################################