We should use bind mounted /home /root /var instead of symlinks during build

Makefile.common

@@ -49,17 +49,23 @@ $(PACKAGES):
 	mount -t proc /proc mnt/proc
 	mount -t sysfs /sysfs mnt/sys
 	mount -t tmpfs /tmp mnt/tmp
-	mount -t tmpfs /tmp mnt/var/tmp
-	mount /dev/$(SECONDARY)1 mnt/build
 	if [ -d mnt/data ] ; then \
 	    mount /dev/$(DISK)4 mnt/data ; \
+	    mount --bind mnt/data/home mnt/home ; \
+	    mount --bind mnt/data/root mnt/root ; \
+	    mount --bind mnt/data/var mnt/var ; \
 	fi
+	mount -t tmpfs /tmp mnt/var/tmp
+	mount /dev/$(SECONDARY)1 mnt/build
 	chroot mnt $(MAKE) -C $(current_dir)$(firstword $(subst ., ,$@)) $(word 2, $(subst ., ,$@))
+	umount -l mnt/var/tmp
 	if [ -d mnt/data ] && [[ $$(findmnt -M mnt/data) ]] ; then \
+	    umount -l mnt/var ; \
+	    umount -l mnt/root ; \
+	    umount -l mnt/home ; \
 	    umount -l mnt/data ; \
 	fi
 	umount -l mnt/build
-	umount -l mnt/var/tmp
 	umount -l mnt/tmp
 	umount -l mnt/sys
 	umount -l mnt/proc