Fixed some out-of-tree build issues

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/tools/gdb/Makefile b/tools/gdb/Makefile
index 632103d..c44cc8a 100644
--- a/tools/gdb/Makefile
+++ b/tools/gdb/Makefile
@@ -47,7 +47,7 @@
 ifeq ($(HOSTOS),cygwin)
 
 all:
-.depend:
+$(obj).depend:
 
 else	# ! CYGWIN