We are starting to require C99 features that can only be supported in
Visual Studio 2013 and later, so we need to prepare rules for Visual Studio
2013 to be our baseline version for Visual Studio builds, so that we can
move the templates from Visual Studio 2010 to Visual Studio 2013.
As this strives to be a shared autotools module between projects, there is
duplication at this point, though, because we still want to support
2008~2012 for projects that do not yet require the C99 features and depends
on GLib-2.50.x/GTK+-3.22.x or earlier.