kbuild: warn if always, hostprogs-y, or hostprogs-m is used

always, hostprogs-y, and hostprogs-m are deprecated.

There is no user in upstream code, but I will keep them for external
modules. I want to remove them entirely someday. Prompt downstream
users for the migration.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/Makefile.lib

@@ -4,8 +4,18 @@ asflags-y  += $(EXTRA_AFLAGS)
 ccflags-y  += $(EXTRA_CFLAGS)
 cppflags-y += $(EXTRA_CPPFLAGS)
 ldflags-y  += $(EXTRA_LDFLAGS)
+ifneq ($(always),)
+$(warning 'always' is deprecated. Please use 'always-y' instead)
 always-y   += $(always)
-hostprogs  += $(hostprogs-y) $(hostprogs-m)
+endif
+ifneq ($(hostprogs-y),)
+$(warning 'hostprogs-y' is deprecated. Please use 'hostprogs' instead)
+hostprogs  += $(hostprogs-y)
+endif
+ifneq ($(hostprogs-m),)
+$(warning 'hostprogs-m' is deprecated. Please use 'hostprogs' instead)
+hostprogs  += $(hostprogs-m)
+endif
 
 # flags that take effect in current and sub directories
 KBUILD_AFLAGS += $(subdir-asflags-y)