Just Base64-encode the value as, say, the make variable B64VAL and do eval "$$(base64dec $(B64VAL))"
in the recipe or in a $(shell ...). If that isn't palatable, invent some other encoding that is more readable. URL encoding: percent hex notation for control and special characters. Quoted printable from MIME is another possibility. You just have a dependency on the decoding tool. Or make up something decodable by an awk or sed one liner. Awk has environment access, and gmake can export.
