bug#46256: [feature/native-comp] AOT eln files ignored if run from build tree

[Eli Zaretskii]

> Cc: 46256@debbugs.gnu.org
> Date: Fri, 26 Feb 2021 20:34:10 +0000
> From:  Andrea Corallo via "Bug reports for GNU Emacs,
>  the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> 
> --- a/src/comp.c
> +++ b/src/comp.c
> @@ -3983,6 +3983,10 @@ DEFUN ("comp-el-to-eln-filename", 
> Fcomp_el_to_eln_filename,
>    if (NILP (Ffile_exists_p (filename)))
>      xsignal1 (Qfile_missing, filename);
>  
> +#ifdef WINDOWSNT
> +  filename = Fw32_long_file_name (filename);
> +#endif

Is "filename" here a name of an existing file?  If not,
Fw32_long_file_name will return nil.