It turns out that UCRT (which is the C runtime that Visual Studio
uses by default these days) quietly changed the semantics for
stat() functions and its variants. Previously they provided data
for the symlink (if the file queried was a symlink), now they
provide data for the target of the symlink.

glib used to call _wstat64() to get certain stat-ish data about
files, such as st_dev, since it was deemed that computing that
data in glib using custom code would be pointless, as _wstat64()
worked just fine.

With UCRT this is no longer true. This commit drops _wstat64() in
favour of a bunch of custom calls that populate the stat buffer
manually. This way glib correctly gets information about a symlink,
not its target.

The _fstat64() call is still being used, as it does not suffer
from this problem and thus remains untouched.