There are a few places where commit 18a33f72 replaced valid (nullable)
(optional) annotations with just (optional). That has a different
meaning.

(nullable) (optional) can only be applied to gpointer* parameters, and
means that both the gpointer* and returned gpointer can be NULL. i.e.
The caller can pass in NULL to ignore the return value; and the returned
value can be NULL.

(optional) can be applied to anything* parameters, and means that the
anything* can be NULL. i.e. The caller can pass in NULL to ignore the
return value. The return value cannot be NULL.
Signed-off-by: Philip Withnall <withnall@endlessm.com>

If we have an input parameter (or return value) we need to use (nullable).
However, if it is an (inout) or (out) parameter, (optional) is sufficient.

It looks like (nullable) could be used for everything according to the
Annotation documentation, but (optional) is more specific.

Various parameter fixups and symbol list additions.

https://bugzilla.gnome.org/show_bug.cgi?id=734888

* Only check __OBJECT_ATTRIBUTES_DEFINED and __UNICODE_STRING_DEFINED
  on MinGW (MSVC doesn't have these)
* MSVC: disable:4005 when including windows.h and ntstatus.h
* Move NTAPI cconv into the parens with the NtQueryKeyFunc
* Fix return values in some functions

https://bugzilla.gnome.org/show_bug.cgi?id=734888

https://bugzilla.gnome.org/show_bug.cgi?id=734888