It turns out that it is possible to use the Windows 8.0 SDK in Visual
Studio 2008 and 2010 officially, but requires a special setup in the
build command prompt.
Tell people how that special setup can be achieved, and restore the
extra instructions on building with Visual Studio 2008, as it is now
possible again.
The roapi.h that is included with the Windows 8.0 SDK mostly works under
plain C with one exception, so let people know the fix for that. Note
that the Windows 8.1 and 10 SDKs contain copies of roapi.h that is
directly usable under plain C.
This release series of GLib began using features that are provided in
the Windows 8 SDK and later for Visual Studio builds. This also means
that it is no longer possible to build GLib with Visual Studio 2008 nor
2010 since the Windows 8+ SDKs do not work with those compiler versions.
Mention that people that still need to use those Visual Studio versions
should continue sticking on to glib-2.66.x, and so remove the section
about the workarounds that need to be applied for Visual Studio 2008
builds, since they are no longer applicable.
