Re: Fix compilation using mingw.org's MinGW

[Eli Zaretskii <eliz@gnu.org>]

> Cc: gdb-patches@sourceware.org
> From: Pedro Alves <palves@redhat.com>
> Date: Fri, 19 Apr 2019 11:51:46 +0100
> 
> building at all either.  The subject for the commit that added that NEWS entry
> sound like that was the intention:
> 
>  commit 742a7df5f4a149f0818aaccfc432c4c0c9a6e26d
>  Author:     Eli Zaretskii <eliz@gnu.org>
>  AuthorDate: Sat Mar 2 15:18:32 2019 +0200
> 
>      GDB no longer supports Windows before XP.
> 
> But surprisingly, I can't find the discussion behind this commit
> in the archives to see the context and what was decided.

The discussion which led to that change is here:

  https://www.sourceware.org/ml/gdb-patches/2019-02/msg00574.html

> >> So shouldn't we instead be setting _WIN32_WINNT to some
> >> appropriate number?
> > 
> > I don't mind, but where?
> 
> I'd do it in common/common-defs.h, before any #include, where we define
> other macros that must be defined before any include, like 
> __STDC_LIMIT_MACROS, _FORTIFY_SOURCE, etc.
> 
> > And also: should we make such changes on the
> > 8.3 branch at this time?
> 
> Not sure.  Off hand I'd think it's pretty safe, but maybe for 8.3
> your patch is safer.

I will try doing this in common-defs.h, but for the branch, we could
set _WIN32_WINNT only in windows-nat.c, as that's the only file that
currently cares, which should be safer.  WDYT?