bug#48354: [PATCH] Fix compat with latest mingw64-headers

[Eli Zaretskii <eliz@gnu.org>]

> Date: Tue, 11 May 2021 12:59:47 +0000
> From: Konstantin Shabanov <mail@etehtsea.me>
> 
> 
> [1:text/plain Hide]
> 
> This commit to mingw-w64 broke compatibility with emacs-head because of the OS_NT conflict:
> 
>     In file included from w32image.c:32:
>     w32common.h:45:3: error: expected identifier before numeric constant
>        45 |   OS_NT
>           |   ^~~~~
> 
> https://sourceforge.net/p/mingw-w64/mingw-w64/ci/dc7ef298837d4581200a3bed660aed36818c1b00/
> 
> The series of patches in attachments should fix the issue:
> - the first one should cause the build to fail in the future instead of silent overriding definition;
> - the second patch renames OS_9X to conform mingw-w64 naming;
> - the third actually fixes build failure (preserving backward compatibility);

Thanks, this is already fixed since 2 days ago on the emacs-27 branch,
soon to be merged to master.