Add simple Makefile to build Docker images

Makefile

@@ -0,0 +1,26 @@
+.PHONY: symbiyosys ghdl-formal NOCACHE
+
+# Support for make environment variable NOCACHE
+ifeq (NOCACHE,$(lastword $(MAKECMDGOALS)))
+    OPTIONS := --no-cache
+    $(info INFO: build without cache)
+    $(eval $(lastword$(MAKECMDGOALS)):dummy;@:)
+endif
+
+NOCACHE:
+	@#
+
+
+ifndef TAG
+    TAG := latest
+    $(info INFO: Using predefined tag 'latest')
+else
+    $(info INFO: Using user given tag '${TAG}')
+endif
+
+all: symbiyosys ghdl-formal
+
+.SECONDEXPANSION:
+symbiyosys ghdl-formal: $$@.Dockerfile
+	docker build ${OPTIONS} -t $@:${TAG} -f $@.Dockerfile .
+	docker build -t $@:latest -f $@.Dockerfile .