bug#54098: 29.0.50; Unexec build broken

[Po Lu]

I get:

In titdic-convert:
international/titdic-cnv.el:473:2: Error: Attempt to modify read-only object: 
(generic dispatches-left methods)
international/titdic-cnv.el:473:2: Error: Invalid function: "
In titdic-convert:
international/titdic-cnv.el:473:2: Error: Attempt to modify read-only object: 
(generic dispatches-left methods)"
Makefile:328: recipe for target
'c:/emacs/emacs-29.0.50/lisp/international/titdic-cnv.elc' failed

When trying to build an unexec build, where, presumably, some more
things in pure space are read only.

Thanks.