Re: Emacs build fails on Windows mingw64

[Eli Zaretskii <eliz@gnu.org>]

> From: Paul Eggert <eggert@cs.ucla.edu>
> Date: Sat, 23 Oct 2021 23:45:04 -0400
> Cc: bug-gnulib@gnu.org, emacs-devel@gnu.org
> 
> On 10/23/21 4:42 PM, Andy Moreton wrote:
> > Can this issue be addressed in gnulib so the emacs bug can be fixed ?
> 
> This appears to be an issue in Emacs not Gnulib, as a few of Emacs's 
> MS-Windows-specific files don't include <config.h> first, which is a 
> documented requirement for Gnulib-using apps. Proposed Emacs patch 
> attached. I haven't tested or installed this, as I don't use MingW.

This solution cannot be used, because ntlib cannot include config.h,
due to various redefinitions and redirections we do in ms-w32.h for
Emacs.  (We could redesign these tricks, but that's a lot of tedium,
and cannot be done on the release branch anyway.)

Let me turn the table and ask why that declaration of strdup is at all
needed in Gnulib's string.h when it's used in MinGW builds?  strdup is
available natively in the MS C runtime, and its prototype is already
in the system's string.h header.  I'm aware that Gnulib has strdup.c,
but we don't currently use it in Emacs, and even if we will at some
point, we won't use it in the MinGW build.  So how about ifdef-ing
that declaration away for MinGW in the Gnulib header?