Add phony target for fast builds

Test: Local build
Change-Id: Ic1df5b7ee5b7ef136e80a97386a6cd5b73aa2331
diff --git a/host_package.mk b/host_package.mk
index 03aa800..bcb6e64 100644
--- a/host_package.mk
+++ b/host_package.mk
@@ -2,6 +2,12 @@
 
 cvd_host_package_tar := $(HOST_OUT)/cvd-host_package.tar.gz
 
+.PHONY: hosttar
+hosttar: $(cvd_host_package_tar)
+
+.PHONY: cf_local_image
+cf_local_image: bootimage cacheimage hosttar systemimage userdataimage vendorimage
+
 ifeq ($(HOST_OS),linux)
 CVD_TAR_FORMAT := --format=gnu
 endif