add openlane clone and build target to openlane/Makefile

openlane/Makefile

diff --git a/openlane/Makefile b/openlane/Makefile
index a9609d3..e63579d 100644
--- a/openlane/Makefile
+++ b/openlane/Makefile
@@ -2,7 +2,8 @@
 CONFIG = $(foreach block,$(BLOCKS), ./$(block)/config.tcl)
 CLEAN = $(foreach block,$(BLOCKS), clean-$(block))
 
-OPENLANE_IMAGE_NAME ?= openlane:rc5
+OPENLANE_TAG ?= rc4
+OPENLANE_IMAGE_NAME ?= openlane:$(OPENLANE_TAG)
 OPENLANE_BASIC_COMMAND = "cd /project/openlane && flow.tcl -design ./$* -save_path .. -save -tag $* -overwrite"
 OPENLANE_INTERACTIVE_COMMAND = "cd /project/openlane && flow.tcl -it -file ./$*/interactive.tcl"
 
@@ -40,6 +41,15 @@
 		$(OPENLANE_IMAGE_NAME) sh -c $(OPENLANE_BASIC_COMMAND);\
 	fi
 
+.PHONY: openlane
+openlane:
+ifeq ($(OPENLANE_ROOT),)
+	@echo "Please export OPENLANE_ROOT"
+	@exit 1
+endif
+	git clone https://github.com/efabless/openlane.git $(OPENLANE_ROOT) && \
+		cd $(OPENLANE_ROOT) && \
+		make openlane
 
 FORCE: