ubuntu-cpc: parallel builds: build hooks during config

* Use series files with dependency handling to generate hook symlinks dynamically

    This patch currently only applies to the "ubuntu-cpc" project.

    More and more logic has been going into the hook scripts to decide
    under which conditions they should run or not. As we are moving
    to parallelized builds of image sets, this will get even more
    complicated. Base hooks will have to know which image sets they
    belong to and modification of the dependency chain between scripts
    will become more complicated and prone to errors, as the number of
    image sets grows.

    This patch, and prior, introduce explicit ordering and dependency
    handling for scripts through the use of `series` files and an
    explicit syntax for dependency specification.

live-build/auto/config

@@ -1053,6 +1053,19 @@ EOF
 	ubuntu-touch:*|ubuntu-touch-custom:*|ubuntu-core:system-image|ubuntu-desktop-next:system-image|ubuntu-cpc:*|ubuntu-server:live)
 		cp -af /usr/share/livecd-rootfs/live-build/${PROJECT}/* \
 			config/
+
+		if [ "$PROJECT" = "ubuntu-cpc" ]; then
+			case ${IMAGE_TARGETS:-} in
+				"")
+					config/hooks.d/make-hooks --hooks-dir config/hooks all
+					;;
+				*)
+					config/hooks.d/make-hooks --hooks-dir config/hooks \
+						"$IMAGE_TARGETS"
+					;;
+			esac
+		fi
+
 		if [ "$IMAGEFORMAT" = none ]; then
 			rm -f config/hooks/*.binary*
 		fi