Fixes the following error with this sample idl:

    #ifdef __WIDL__
    #pragma winrt ns_prefix
    #endif

    import "wtypes.idl";

    namespace Windows {
        [object]
        interface IFoo {}

        [object]
        interface IBar { HRESULT DoBar([in] IFoo *foo); }
    }

$ widl -o windows.foo.h windows.foo.idl
windows.foo.idl:13: error: type 'IFoo' not found
Signed-off-by: Rémi Bernon <rbernon@codeweavers.com>
Signed-off-by: Alexandre Julliard <julliard@winehq.org>