Here are the steps that worked for me to build the kernel package for Freenix 14.2. I'm not sure which is the recommended way how to do it, though.
1. Download the build scripts from the command line prompt as non-root user:
lftp -c "open https://freenix.net/fxp/freeslack64-14.2/source/fxp/build/; mirror linux-libre" && cd linux-libre
curl https://freenix.net/fxp/freeslack64-14.2/source/fxp/build/linux-libre/README > README.TXT
2. Get the source of the latest 4.4.x kernel version and install it manually, without building a package:
Set a variable for the download path we use later on:
Find the latest 4.4.x kernel source and put it to another variable:
Set a version variable:
SRC_ARCH=`curl -s $SRC_URL/ | egrep -o "linux-libre-4\.4\.[0-9]+-gnu.tar.bz2" | head -n1`
Download the source archive:
VERSION=`egrep -o "4\.4\.[0-9]+" <<<$SRC_ARCH`
Unpack the source archive to /usr/src/:
su -c "cd /usr/src; tar -xvf "`pwd`"/$SRC_ARCH && ln -sv linux-$VERSION linux"
3. Copy the downloaded config files to /usr/src/:
su -c "cp -v config-generic-4.4.*.x64 /usr/src/linux/config-generic && cp -v config-huge-4.4.*.x64 /usr/src/linux/config-huge"
4. Build the kernel image package:
su - -c "cd "`pwd`"; bash linux-libre-image.SlackBuild"
5. Read the downloaded README.TXT for instructions on further installation steps.
I didn't use the linux-libre-source.SlackBuild script, since it doesn't extract the kernel source archive but only copies it to /usr/src/, and I don't know what's the benefit of installing a Package, which copies an archive that isn't used by any program or script, and only becomes usable after extracting it manually, and also other steps are needed, like copying the config files and the README.TXT, in order to work with the image build script.
I hope this helps.