bug#48342: native-comp emacs gets into an infinite loop at startup if no .el files are available

[Eli Zaretskii]

> From: Dima Kogan <dima@secretsauce.net>
> Cc: akrl@sdf.org, 48342@debbugs.gnu.org
> Date: Tue, 11 May 2021 10:29:20 -0700
> 
> The maybe_swap_for_el() call in Frame #28 checks for the sources, sees
> that the file on disk doesn't exist, and throws the warning as expected:
> 
> Code:
>   call2 (intern_c_string ("display-warning")
> Full context:
>   
> https://github.com/emacs-mirror/emacs/blob/bb8b8d717f91a85ca41de9e82246e6975e1ed719/src/lread.c#L1713
> 
> Frame #26 is the (display-warning ...)
> 
> Frame #25 is (autoload-do-load ... 'display-warning)
> 
> Frame #23 is (load "warnings" ...)
> 
> The backtrace isn't right about the line number in frame #22, but that
> function is in lread.c. It's trying to compile "warnings.el".

I guess when we find that a source for some .elc file is not
available, we should add its .el name to
native-comp-deferred-compilation-deny-list?