Keeping my notes findable: Rmutt on MacOSX will build cleanly if you change the CC line in the Makefile to be:
CC = gcc -arch x86_64
That is all. For those who haven’t tried it, Rmutt is a grammar-based nonsense generator along the lines of the Dada Engine (see also Web version). The Dada Engine powers the near-legendary Postmodernism Generator, though I’m lately thinking about putting these kinds of tools into a hosted (openid/wiki etc) environment where people could collaboratively build up shared grammars.