testing: Improve building different revisions of Git-recipes

If we check out and build a certain revision of a dependency in a branch and
switch to another that requires a different revision and then switch back,
the previous approach installed the wrong revision as it would incorrectly
assume the required revision was already built and ready to install.

testing/scripts/recipes/006_tkm-rpc.mk

@@ -16,11 +16,11 @@ all: install
 
 .$(PKG)-checkout-$(REV): .$(PKG)-cloned
 	cd $(PKG) && git fetch && git checkout $(REV)
-	@touch $@
+	@rm -f .$(PKG)-checkout-* && touch $@
 
 .$(PKG)-built-$(REV): .$(PKG)-checkout-$(REV)
 	cd $(PKG) && make
-	@touch $@
+	@rm -f .$(PKG)-built-* && touch $@
 
 install: .$(PKG)-built-$(REV)
 	cd $(PKG) && make PREFIX=$(PREFIX) install