bug#18302: MSYS2 build issues

[Eli Zaretskii <eliz@gnu.org>]

> Date: Thu, 21 Aug 2014 17:29:51 -0400
> From: Ken Brown <kbrown@cornell.edu>
> CC: karol.ostrovsky@gmail.com, chriszheng99@gmail.com, 18302@debbugs.gnu.org
> 
> >    #if defined __CYGWIN__ && !defined HAVE_X_WINDOWS
> >    #include <noX/xpm.h>
> >    #else
> >    #include <X11/xpm.h>
> >    #endif
> 
> I neglected to say that xpm.h in /usr/include/noX is actually a symlink 
> to /usr/include/noX/X11/xpm.h.

I don't see how this changes anything.  You could use

  #include <noX/X11/xpm.h>

or you could remain with <noX/xpm.h>, they both will work.

> The code that includes xpm.h (in 
> image.c) is '#include "X11/xpm.h"' on all platforms.  For the native 
> Windows build and the Cygwin w32 build, this is done conditionally on 
> NTGUI, after first defining some macros.  In order for "X11/xpm.h" to 
> produce the correct file, the include path has to be set up correctly. 

That just means we need to re-arrange the #ifdef's a bit differently.
Clearly, not rocket science.

> I really don't want to rewrite all this for no good reason.

As I said, this is your call.  My point is that adding
system-dependent -I switches in configure is not the only way, and IMO
not the best one.

> > The way we work around the problem now will break if someone installs
> > the standard header files in a place other than /usr/include.
> 
> In the Cygwin case, I'm not sure what you mean by "someone".

The end-user, of course.  Posix platforms don't limit end-users in
where they install their header files, and GCC supports that.

> I'll add a comment to configure.ac on the trunk.

Thanks, but why not on the release branch?  A comment cannot possibly
do any harm.