target/arm: define stub library

target/arm: define stub library

We use the mechanic introduced in previous commit to define a arm stubs
library. With this, we are able to eliminate symbol conflicts when
linking arm and aarch64 targets, and get one step closer to having a
single-binary.

Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20260424230103.1579600-3-pierrick.bouvier@oss.qualcomm.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>