Suppress warnings for systems that do not recognize LFS_*.

 getconf: no such configuration parameter `LFS_CFLAGS'
 getconf: no such configuration parameter `LFS_LDFLAGS'
 getconf: no such configuration parameter `LFS_LIBS'

Fixes: d7f14c66c273 ("kbuild: Enable Large File Support for hostprogs")
Reported-by: Chen Feng <puck.chen@hisilicon.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>