bug#53678: 29.0.50; Invalid read syntax: "#<" for package install in Windows

[Eli Zaretskii]

> Date: Tue, 01 Feb 2022 13:32:11 +0800
> From:  Shuguang Sun via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> When I try to install packages from the Package Menu or the command of
> package-install since about two weeks ago, it reports the error:
> ```
> error in process sentinel: async-when-done: Invalid read syntax: "#<"
> error in process sentinel: Invalid read syntax: "#<"
> ```
> And it seems not preventing the installation process but stops the emacs
> to compile the el files to elc.
> 
> FYI. I failed to find out what makes it. It looks like the local variable in
> the autoloads file generated by the package process. It add
> `;; coding: utf-8-emacs-unix`, however, in windows, the file is probablly
> in a coding of utf-8-emacs-dos. When I try to open the autoload file,
> Emacs can't regonize the major mode which assumes to be `emacs-lisp-mode`.
> Unless I change the `;; coding: utf-8-emacs-unix` to
> `;; coding: utf-8-emacs`, it can be open in the `emacs-lisp-mode`.

Stefan, any thoughts?