bug#49651: 28.0.50; setf bug

[Stefan Monnier]

>> `push` and `pop` go through some extra efforts to avoid loading
>> `gv` when the PLACE is trivial enough.
> Right.  Well, then we can't really move them to gv.el either,

Of course, we can.

> because that would break code that says
>
> (require 'cl-lib)
> (setf (getenv ...))
>
> since
>
> (progn
>   (require 'cl-lib)
>   (featurep 'gv)) => nil

`setf` is defined in `gv.el`!


        Stefan