testing: Avoid unnecessary rebuilds of components built from Git repos

Installing apparently changes the timestamp on the repo dir triggering make
to checkout and build the whole thing again.

testing/scripts/recipes/009_xfrm-proxy.mk

@@ -8,14 +8,15 @@ export ADA_PROJECT_PATH=/usr/local/ada/lib/gnat
 
 all: install
 
-$(PKG):
-	git clone $(SRC) $(PKG)
+.$(PKG)-cloned:
+	[ -d $(PKG) ] || git clone $(SRC) $(PKG)
+	@touch $@
 
-.$(PKG)-cloned-$(REV): $(PKG)
+.$(PKG)-checkout-$(REV): .$(PKG)-cloned
 	cd $(PKG) && git fetch && git checkout $(REV)
 	@touch $@
 
-.$(PKG)-built-$(REV): .$(PKG)-cloned-$(REV)
+.$(PKG)-built-$(REV): .$(PKG)-checkout-$(REV)
 	cd $(PKG) && make
 	@touch $@