This is never shown because include/asm-$(ARCH)/Kbuild does not exist.

headers_check does not make any sense for barebox.

Linux also deprecated headers_check by commit 7ecaf069da52 ("kbuild:
move headers_check rule to usr/include/Makefile").

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>