win32: remove usage of attribute gcc_struct

win32: remove usage of attribute gcc_struct

This attribute is not recognized by clang.

An investigation has been performed to ensure this attribute has no
effect on layout of structures we use in QEMU [1], so it's safe to
remove now.

In the future, we'll forbid introducing new bitfields in packed struct,
as they are the one potentially impacted by this change.

[1] https://lore.kernel.org/qemu-devel/66c346de-7e20-4831-b3eb-1cda83240af9@linaro.org/

Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Acked-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Stefan Weil <sw@weilnetz.de>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20250110203401.178532-2-pierrick.bouvier@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20250116160306.1709518-24-alex.bennee@linaro.org>