Update config.h.win32.in

Make entries more in sync with the items checked with autotools, and
provide a MinGW declaration for _GLIB_EXTERN, taken from configure.ac.
GIO MSVC Project: Link to iphlpapi.lib

This is needed for GetAdaptersAddresses()[1], which was used to implement
if_nametoindex on Windows, notably on Windows XP, in commit 01156b12.

if_nametoindex and if_indextoname, as noted in config.h.win32(.in), is
available with Windows Vista and later, so when we eventually drop
support for Windows XP, we can call them directly, and these functions
also reside in the same iphlpapi.lib

[1]: http://msdn.microsoft.com/en-us/library/windows/desktop/aa365915%28v=vs.85%29.aspx