kbuild: suppress warnings from 'getconf LFS_*'

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: d7f14c66c2 ("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>

Makefile

@@ -353,9 +353,9 @@ CONFIG_SHELL := $(shell if [ -x "$$BASH" ]; then echo $$BASH; \
 	  else if [ -x /bin/bash ]; then echo /bin/bash; \
 	  else echo sh; fi ; fi)
 
-HOST_LFS_CFLAGS := $(shell getconf LFS_CFLAGS)
-HOST_LFS_LDFLAGS := $(shell getconf LFS_LDFLAGS)
-HOST_LFS_LIBS := $(shell getconf LFS_LIBS)
+HOST_LFS_CFLAGS := $(shell getconf LFS_CFLAGS 2>/dev/null)
+HOST_LFS_LDFLAGS := $(shell getconf LFS_LDFLAGS 2>/dev/null)
+HOST_LFS_LIBS := $(shell getconf LFS_LIBS 2>/dev/null)
 
 HOSTCC       = gcc
 HOSTCXX      = g++