bug#57386: 29.0.50; support make-symbolic-link without admin priviledge on Windows

[Eli Zaretskii]

> From: Kiên Nguyễn Quang
>  <kien.n.quang@gmail.com>
> Date: Thu, 25 Aug 2022 00:33:58 +0900
> 
> The CreateSymbolicLink Win32API has a flag that allows creating sym-links 
> without admin privileges
> SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE.
> This patch added that support for w32 Emacs.

Thanks, but we cannot use that flag unconditionally, because it is not
supported on all Windows versions.  The addition of the flags should
be conditioned on the version of Windows on which Emacs runs.