build system: fix another cbfstool race

It just doesn't work to have files depend on their parent
directory: As soon as the files are written, the time stamp
of the directory changes, too.

This led to spurious updates of cbfstool and rmodtool, and
related "permission denied" errors when linker and build
system ran into each other.

Change-Id: I44a7d7b4b1d47a1567ece1f57dfd6745d05ee651
Signed-off-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-on: http://review.coreboot.org/6276
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
diff --git a/util/cbfstool/Makefile.inc b/util/cbfstool/Makefile.inc
index 0548ea4..410d96c 100644
--- a/util/cbfstool/Makefile.inc
+++ b/util/cbfstool/Makefile.inc
@@ -27,9 +27,6 @@
 TOOLFLAGS+=-mno-ms-bitfields
 endif
 
-$(objutil)/cbfstool:
-	mkdir -p $@
-
 $(objutil)/cbfstool/%.o: $(top)/util/cbfstool/%.c
 	printf "    HOSTCC     $(subst $(objutil)/,,$(@))\n"
 	$(HOSTCC) $(TOOLFLAGS) $(HOSTCFLAGS) -c -o $@ $<
@@ -42,10 +39,10 @@
 	printf "    HOSTCC     $(subst $(objutil)/,,$(@))\n"
 	$(HOSTCC) $(TOOLFLAGS) $(HOSTCFLAGS) -c -o $@ $<
 
-$(objutil)/cbfstool/cbfstool: $(objutil)/cbfstool $(addprefix $(objutil)/cbfstool/,$(cbfsobj))
+$(objutil)/cbfstool/cbfstool: $(addprefix $(objutil)/cbfstool/,$(cbfsobj))
 	printf "    HOSTCC     $(subst $(objutil)/,,$(@)) (link)\n"
 	$(HOSTCC) $(TOOLFLAGS) -o $@ $(addprefix $(objutil)/cbfstool/,$(cbfsobj))
 
-$(objutil)/cbfstool/rmodtool: $(objutil)/cbfstool $(addprefix $(objutil)/cbfstool/,$(rmodobj))
+$(objutil)/cbfstool/rmodtool: $(addprefix $(objutil)/cbfstool/,$(rmodobj))
 	printf "    HOSTCC     $(subst $(objutil)/,,$(@)) (link)\n"
 	$(HOSTCC) $(TOOLFLAGS) -o $@ $(addprefix $(objutil)/cbfstool/,$(rmodobj))