bug#48221: 28.0.50; defsubsts aren't native compiled?

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Date: Wed, 05 May 2021 11:36:02 +0200
> Cc: 48221@debbugs.gnu.org
> 
> (A related question -- is (boundp 'comp-ctxt) really the best way to
> test for whether we have a native-compiled Emacs?  That's just a defvar
> in comp-cstr.el...)

We could perhaps provide 'native-compilation in comp.c?  WDYT?