kernel/linux: symlink custom kernel source dir with '-f'

build fails to symlink to custom kernel dir when the build is not the first time
because of 'ln -s' without '-f' option.

Signed-off-by: "Jang, Bongseo" <graycells@gmail.com>
Message-ID: <543e2981f2b723ecd850.1348370892@localhost.localdomain>
PatchWork-ID: 186178

#!/bin/sh

# Needed for systems without gettext

$* -xc -o /dev/null - > /dev/null 2>&1 << EOF

#include <libintl.h>

int main()

{

	gettext("");

	return 0;

}

EOF

if [ ! "$?" -eq "0"  ]; then

	echo -DKBUILD_NO_NLS;

fi