kbuild: treat an object as multi-used when $(foo-) is set

Currently, Kbuild treats an object as multi-used when any of
$(foo-objs), $(foo-y), $(foo-m) is set. It makes more sense to
check $(foo-) as well.

In the context of foo-$(CONFIG_FOO_FEATURE1), CONFIG_FOO_FEATURE1
could be unset.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/Makefile.lib

@@ -41,9 +41,9 @@ obj-m		:= $(filter-out %/, $(obj-m))
 # Subdirectories we need to descend into
 subdir-ym	:= $(sort $(subdir-y) $(subdir-m))
 
-# if $(foo-objs), $(foo-y), or $(foo-m) exists, foo.o is a composite object
-multi-used-y := $(sort $(foreach m,$(obj-y), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))), $(m))))
-multi-used-m := $(sort $(foreach m,$(obj-m), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y)) $($(m:.o=-m))), $(m))))
+# If $(foo-objs), $(foo-y), $(foo-m), or $(foo-) exists, foo.o is a composite object
+multi-used-y := $(sort $(foreach m,$(obj-y), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y)) $($(m:.o=-))), $(m))))
+multi-used-m := $(sort $(foreach m,$(obj-m), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y)) $($(m:.o=-m)) $($(m:.o=-))), $(m))))
 multi-used   := $(multi-used-y) $(multi-used-m)
 
 # $(subdir-obj-y) is the list of objects in $(obj-y) which uses dir/ to
@@ -52,8 +52,8 @@ subdir-obj-y := $(filter %/built-in.a, $(obj-y))
 
 # Replace multi-part objects by their individual parts,
 # including built-in.a from subdirectories
-real-obj-y := $(foreach m, $(obj-y), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y))),$($(m:.o=-objs)) $($(m:.o=-y)),$(m)))
-real-obj-m := $(foreach m, $(obj-m), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y)) $($(m:.o=-m))),$($(m:.o=-objs)) $($(m:.o=-y)) $($(m:.o=-m)),$(m)))
+real-obj-y := $(foreach m, $(obj-y), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y)) $($(m:.o=-))),$($(m:.o=-objs)) $($(m:.o=-y)),$(m)))
+real-obj-m := $(foreach m, $(obj-m), $(if $(strip $($(m:.o=-objs)) $($(m:.o=-y)) $($(m:.o=-m)) $($(m:.o=-))),$($(m:.o=-objs)) $($(m:.o=-y)) $($(m:.o=-m)),$(m)))
 
 # DTB
 # If CONFIG_OF_ALL_DTBS is enabled, all DT blobs are built