bug#24613: Windows build with rsvg fails on newest MinGW

[Eli Zaretskii <eliz@gnu.org>]

> From: Nikolay Kudryavtsev <nikolay.kudryavtsev@gmail.com>
> Date: Tue, 4 Oct 2016 15:12:07 +0300
> 
> I've been trying to get rsvg working and here's what I found:

I don't see how anything in what you see is related to rsvg, what am I
missing?

> > In file included from c:\mingw\include\wchar.h:212:0,
> >                  from c:\mingw\include\iconv.h:106,
> >                  from C:/MinGW/include/libxml2/libxml/encoding.h:28,
> >                  from C:/MinGW/include/libxml2/libxml/parser.h:807,
> >                  from C:/MinGW/include/libxml2/libxml/globals.h:18,
> >                  from C:/MinGW/include/libxml2/libxml/threads.h:35,
> >                  from C:/MinGW/include/libxml2/libxml/xmlmemory.h:218,
> >                  from C:/MinGW/include/libxml2/libxml/tree.h:1248,
> >                  from d:/Emacs/source/emacs-25.1/src/xml.c:23:
> > c:\mingw\include\sys/stat.h:173:8: error: redefinition of 'struct _stat'
> >  struct _stat __struct_stat_defined( _off_t, time_t );
> >         ^
> > In file included from d:/Emacs/source/emacs-25.1/nt/inc/ms-w32.h:440:0,
> >                  from d:/Emacs/source/emacs-25.1/src/conf_post.h:32,
> >                  from ./config.h:1916,
> >                  from d:/Emacs/source/emacs-25.1/src/xml.c:19:
> > d:/Emacs/source/emacs-25.1/nt/inc/sys/stat.h:106:8: note: originally 
> > defined here
> >  struct _stat
> >         ^

So wchar.h now includes sys/stat.h?  What MinGW runtime are you using
and where did you download it?

Does it help to add the following to nt/inc/sys/stat.h?

#ifndef _SYS_STAT_H
#define _SYS_STAT_H
#endif

The best solution in the long run is to stop redefining struct stat
and friends, and instead call it something else (since we don't use
the MS implementation of 'stat' and 'fstat' anyway).  Patches to that
effect are welcome.