use $_extraopts on mksquashfs

this is a new prefered behaviour since we don't always want to imply x86
optimization to the squashfs

zlibs/bootstrap

@@ -207,11 +207,12 @@ EOF
 	for i in $inittab; do
 		grep -q "^$i" $strapdir/etc/inittab && continue
 		print "$i" | sudo tee -a $strapdir/etc/inittab >/dev/null
+	done
 
 	for i in $custmodules; do
 		grep -q "^$i" $strapdir/etc/modules && continue
 		print "$i" | sudo tee -a $strapdir/etc/modules >/dev/null
-	done || return 0
+	done
 
-	[[ -n "$TAR_STAGE4" ]] bootstrap_tar_pack "$bootstrap_tgz_stage4"
+	[[ -n "$TAR_STAGE4" ]] && bootstrap_tar_pack "$bootstrap_tgz_stage4"
 }

zlibs/iso

@@ -103,9 +103,14 @@ iso_squash_strap() {
 
 	notice "creating squashfs out of strapdir"
 
+	_extraopts=()
+	if [[ "$arch" = amd64 ]]; then
+		_extraopts+=(-Xbcj x86)
+	fi
+
 	pushd $workdir
 	sudo mksquashfs $strapdir binary/live/filesystem.squashfs \
-		-Xbcj x86 -noappend -comp xz || zerr
+		${_extraopts} -noappend -comp xz || zerr
 	popd
 	unset uefi_opt
 }