Kbuild: Makefile.modbuiltin: include auto.conf and tristate.conf mandatory

The files auto.conf and tristate.conf are mandatory for building
modules.builtin files, therefore include them as such.

Usually, the top-level Makefile ensures that those files exist but we
want to make sure we get noticed if they are missing for whatever
reason.
Signed-off-by: Dirk Gouders <dirk@gouders.net>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/Makefile.modbuiltin

@@ -8,10 +8,10 @@ src := $(obj)
 PHONY := __modbuiltin
 __modbuiltin:
 
--include include/config/auto.conf
+include include/config/auto.conf
 # tristate.conf sets tristate variables to uppercase 'Y' or 'M'
 # That way, we get the list of built-in modules in obj-Y
--include include/config/tristate.conf
+include include/config/tristate.conf
 
 include scripts/Kbuild.include