Use host tools from build container

Instead of building host tools along with the target packages, we now
rely on the build container to contain everything we need to build Aimee
OS.  The _aimee-os.org/build/build-{target}_ image (tentative name)
includes a cross-compilation toolchain and all of the tools that were
originally listed in `host-tools.packages`.

Makefile

@@ -17,16 +17,6 @@ $(O)/.prepared: \
 
 prepare: $(O)/.prepared
 
-$(O)/.host-tools: \
-		build-host-tools.sh \
-		host-tools.packages \
-		$(shell find $(CONFIGDIR)/portage/host -type f) \
-		$(O)/.prepared
-	./build-host-tools.sh
-	touch $(O)/.host-tools
-
-host-tools: $(O)/.host-tools
-
 $(O)/.built: \
 		build.sh \
 		build.packages \
@@ -34,7 +24,6 @@ $(O)/.built: \
 		$(CONFIGDIR)/build.packages \
 		$(CONFIGDIR)/install.packages \
 		$(shell find $(CONFIGDIR)/portage/target -type f) \
-		$(O)/.host-tools \
 		$(O)/.prepared
 	./build.sh
 	touch $(O)/.built
@@ -56,7 +45,6 @@ $(O)/.ready: \
 		$(O)/semanage.mods \
 		$(shell find overlay -type f) \
 		$(shell find $(CONFIGDIR)/overlay -type f 2>/dev/null) \
-		$(O)/.host-tools \
 		$(O)/.built
 	./build-rootfs.sh "$(O)"
 	touch $(O)/.ready
@@ -83,7 +71,6 @@ squashfs: $(IMAGESDIR)/rootfs.squashfs
 $(O)/linux/arch/arm64/boot/Image.gz: \
 		build-kernel.sh \
 		$(CONFIGDIR)/linux.config \
-		$(O)/.host-tools \
 		$(O)/.prepared
 	./build-kernel.sh "$(O)"
 
@@ -92,7 +79,6 @@ kernel: $(O)/linux/arch/arm64/boot/Image.gz
 $(O)/efi-part/EFI/BOOT/BOOTAA64.efi: \
 		build-grub.sh \
 		grub.cfg \
-		$(O)/.host-tools \
 		$(O)/.prepared
 	./build-grub.sh "$(O)"
 
@@ -115,18 +101,16 @@ $(IMAGESDIR)/update.tar.zstd: \
 		$(IMAGESDIR)/rootfs.squashfs \
 		$(IMAGESDIR)/firmware.img \
 		install-update.sh \
-		$(O)/.host-tools \
 		$(O)/.prepared
 	./build-update.sh "$(IMAGESDIR)"
 
 clean:
 	rm -rf $(O)/linux $(O)/output $(IMAGESDIR) $(O)/tmp
-	rm -f $(O)/.prepared $(O)/.host-tools
+	rm -f $(O)/.prepared
 
 .PHONY: \
 	build \
 	grub \
-	host-tools \
 	kernel \
 	prepare \
 	sdcard.img \