Allow running validate-via-docker-all with -j

Author: phadej

Makefile

@@ -112,26 +112,18 @@ cabal-install-test:
 
 # Docker validation
 
-validate-via-docker-all :
-	@echo "This takes a lot of time"
-	@echo 5
-	@sleep 1
-	@echo 4
-	@sleep 1
-	@echo 3
-	@sleep 1
-	@echo 2
-	@sleep 1
-	@echo 1
-	@sleep 1
-	$(MAKE) validate-via-docker-7.6.3
-	$(MAKE) validate-via-docker-7.8.4
-	$(MAKE) validate-via-docker-7.10.3
-	$(MAKE) validate-via-docker-8.0.2
-	$(MAKE) validate-via-docker-8.2.2
-	$(MAKE) validate-via-docker-8.4.4
-	$(MAKE) validate-via-docker-8.6.5
-	$(MAKE) validate-via-docker-8.8.1
+# Use this carefully, on big machine you can say
+#
+#   make validate-via-docker-all -j4 -O
+#
+validate-via-docker-all : validate-via-docker-7.6.3
+validate-via-docker-all : validate-via-docker-7.8.4
+validate-via-docker-all : validate-via-docker-7.10.3
+validate-via-docker-all : validate-via-docker-8.0.2
+validate-via-docker-all : validate-via-docker-8.2.2
+validate-via-docker-all : validate-via-docker-8.4.4
+validate-via-docker-all : validate-via-docker-8.6.5
+validate-via-docker-all : validate-via-docker-8.8.1
 
 validate-via-docker-7.6.3:
 	docker build -t cabal-validate -f .docker/validate-7.6.3.dockerfile .