kconfig: split menu.c out of parser.y

Compile menu.c as an independent compilation unit.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
diff --git a/scripts/kconfig/internal.h b/scripts/kconfig/internal.h
new file mode 100644
index 0000000..2f7298c
--- /dev/null
+++ b/scripts/kconfig/internal.h
@@ -0,0 +1,9 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef INTERNAL_H
+#define INTERNAL_H
+
+struct menu;
+
+extern struct menu *current_menu, *current_entry;
+
+#endif /* INTERNAL_H */