bug#7848: 23.2.91; Can't build with MinGW

[Eli Zaretskii]

> From: Stefan Monnier <monnier@iro.umontreal.ca>
> Cc: Kazuhiro Ito <kzhr@d1.dion.ne.jp>,  7848@debbugs.gnu.org
> Date: Sat, 15 Jan 2011 23:41:51 -0500
> 
> > Sorry.  Please try replacing this:
> 
> >   SET_SYMBOL_VAL (XSYMBOL (Qlibpng_version), make_number (PNG_LIBPNG_VER));
> [...]
> >   XSYMBOL (Qlibpng_version)->value = make_number (PNG_LIBPNG_VER);
> 
> I would recommend to stay away from such low-level code unless you're
> writing code that tries to implement part of the binding-semantics
> of Emacs.  I.e. just use Fset.

Using Fset here would be a terrible overkill, IMO.  I'm not even sure
I understand all of its semantics, and not sure it will work correctly
in the context of an init_* function that is called when Emacs is
dumped.  OTOH, direct assignments of symbol's value like above _are_
used in several init_* functions and elsewhere.

Also, I wanted to un-break the release branch as fast as I could.

Having said all that, feel free to change what I did to use Fset, both
on the branch and on the trunk.