kbuild: warn when a moduled uses a symbol marked UNUSED

We now have infrastructure in place to mark an EXPORTed symbol
as unused. So the natural next step is to warn during buildtime when
a module uses a symbol marked UNUSED.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/scripts/mod/modpost.h b/scripts/mod/modpost.h
index 2b00c60..d398c61 100644
--- a/scripts/mod/modpost.h
+++ b/scripts/mod/modpost.h
@@ -117,7 +117,9 @@
 	Elf_Sym      *symtab_start;
 	Elf_Sym      *symtab_stop;
 	Elf_Section  export_sec;
+	Elf_Section  export_unused_sec;
 	Elf_Section  export_gpl_sec;
+	Elf_Section  export_unused_gpl_sec;
 	Elf_Section  export_gpl_future_sec;
 	const char   *strtab;
 	char	     *modinfo;