If you want exactly what make unstage1 did, "make stage1-start". There is also "make restrap" as in the old scheme.
Thanks. A side note: I've always been extremely confused by the "unstageN" and "stageN" targets in the gcc directory. The double usage of "stage" as noun and verb was complicating things, also because I'm not a native speaker and the meaning of "to stage" as "to set aside" is not in my dictionary. Interesting. In all the years I've been using those targets, I never even thought about the verb meaning of "stage". I wonder if the folks who named those targets ever did.