bug#47162: Mouse Wheel Won't Work When Emacs Built without Any Window System

[Eli Zaretskii]

> From: Lars Ingebrigtsen <larsi@gnus.org>
> Cc: Stefan Monnier <monnier@iro.umontreal.ca>,  contovob@tcd.ie,
>   johnson9009@163.com,  47162@debbugs.gnu.org
> Date: Sat, 31 Jul 2021 16:14:31 +0200
> 
>   ;; We'd like to use custom-initialize-set here so the setup is done
>   ;; before dumping, but at the point where the defcustom is evaluated,
>   ;; the corresponding function isn't defined yet, so
>   ;; custom-initialize-set signals an error.
>   :initialize 'custom-initialize-delay
> 
> It's there because we (in some configurations) dump Emacs with mwheel.
> But it causes problems when we're not dumping it.

Why does this need to be done via custom-initialize-delay?  Why can't
we simply call the necessary code at startup, explicitly, when mwheel
is available?