t and nil in pure memory?

[Dan Nicolaescu]

The last GC before dumping generates 200K calls to mark_object, of those
20K have Qt or Qnil as an argument.

Would it make sense to put Qt and Qnil in pure memory?

We don't have any function that can create pure symbols.

Moving Qt and Qnil in pure memory would break things like:

(put t 'foo 'bar)

but maybe this works by accident rather than design.

How about other things that have SYMBOL_CONSTANT_P() set to 1?  Can they
go to pure memory?

More generally it would be very good to be able to put symbols in pure
memory, about 1/3 of the mark_object calls are for symbols, and it does
not seem that it's too useful to GC `car', `cdr', etc.  But it does not
seem to be too easy to do :-(