Suppress "nothing to override" on equals, hashCode, toString

This is needed to smoothly make equals, hashCode and toString members of Any
instead of being extensions, as they are now: according to our bootstrapping
process, the same compiler code will be built twice, by old compiler (with
extensions) and by new compiler (with members). In the resulting code
'override' should be on all these members in all classes, so the old compiler
should be able to compile such code