Add a phony "nothing" goal that reads the makefiles but doesn't try to build anything.

Change-Id: Idac551e5c796321e993b94761f5cbf5b55c1a994
diff --git a/core/main.mk b/core/main.mk
index 49367ec..5f94c63 100644
--- a/core/main.mk
+++ b/core/main.mk
@@ -903,3 +903,7 @@
 .PHONY: showcommands
 showcommands:
 	@echo >/dev/null
+
+.PHONY: nothing
+nothing:
+	@echo Successfully read the makefiles.