make-ext4-fs: enable parallel compression for zstd

... as done in a couple of other image builders already

DavHau 2ec06a51 b5b9c20c

Changed files
+1 -1
nixos
+1 -1
nixos/lib/make-ext4-fs.nix
···
if [ ${builtins.toString compressImage} ]; then
echo "Compressing image"
-
zstd -v --no-progress ./$img -o $out
+
zstd -T$NIX_BUILD_CORES -v --no-progress ./$img -o $out
fi
'';
}