target-info: add multi-target test binary

Now we are able to link multiple targets together, we want to make sure
no build regression is introduced. For this, add a new unit test linking
compatible targets.

In addition, we check QOM types can be initialized, ensuring uniqueness
among all targets.

For now, supported targets are:
- arm-softmmu
- aarch64-softmmu
- microblaze-softmmu

Signed-off-by: Pierrick Bouvier <pierrick.bouvier@oss.qualcomm.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
Message-ID: <20260921204954.50529-3-pierrick.bouvier@oss.qualcomm.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>