bug#48021: comp.el cannot be loaded without native compilation

[Glenn Morris]

Package: emacs
Version: 28.0.50

At b7c22fab7d, in a default build:

./src/emacs -Q -l ./lisp/emacs-lisp/comp.el

   memq: Symbol's value as variable is void: comp-ctxt

(Presumably it works if --with-native-compilation is used.)

This causes test failures for custom tests, and multiple failures for
comp-cstr-tests (perhaps those should be tagged :nativecomp, I don't know.)

Ref eg https://hydra.nixos.org/build/142074384