Introduce the multiboot target

This target may be used to create an empty multiboot image (only the
bootloader is installed). This is intended to be used manually to
either debug the crucial part of the bootloader installation, or just
because a multiboot image comes in handy for another purpose.

Makefile

@@ -455,6 +455,24 @@ $(IMAGE_DIR)$(GRUB_INSTALL_DIR)/lipinfo.cfg : | $(WORKSPACE)
 
 image : image_content $(GRUB_ASSEMBLE_DIR)/mbr.img
 
+#The following target is not used by lipck itself. It may be used to create
+#an empty (only the bootloader will be installed) manually. In particular,
+#it can be used to test the image creation process of lipck (it is not
+#necessary to remaster an image to test this crucial base part).
+multiboot :
+	$(MAKE) "IMAGE_PART_FILE=$(WORKSPACE)/multiboot.part" image_skel_file
+	mkdir -p "$(WORKSPACE)/multiboot.work"
+	mount "$(WORKSPACE)/multiboot.part" "$(WORKSPACE)/multiboot.work"
+	$(MAKE) "IMAGE_DIR=$(WORKSPACE)/multiboot.work" image_grub_install \
+		|| (umount "$(WORKSPACE)/multiboot.work" && exit 1)
+	#since this is most likely a standalone image make the lipck grubx64 the
+	#default bootloader for 64bit efi systems
+	mv "$(WORKSPACE)/multiboot.work/efi/boot/"{grubx64-unsigned.efi,bootx64.efi} \
+		|| (umount "$(WORKSPACE)/multiboot.work" && exit 1)
+	umount "$(WORKSPACE)/multiboot.work"
+	$(MAKE) "IMAGE_PART_FILE=$(WORKSPACE)/multiboot.part" IMAGE_FILE=MultiBoot.img \
+		image_assemble
+
 gparted : $(call archdir,$(PRIMARY_ARCH))/gparted-live.iso $(call archdir,$(SECONDARY_ARCH))/gparted-live.iso
 $(call gentargets,/gparted-live.iso) :
 	wget -O "$@" "$(GPARTED_BASE_URL)/gparted-live-$(GPARTED_VERSION)-$(subst $(SECONDARY_ARCH),i686-pae,$(subst $(PRIMARY_ARCH),amd64,$*)).iso"