tests/functional: Introduce the dso_suffix() helper

tests/functional: Introduce the dso_suffix() helper

Introduce a helper to get the default shared library
suffix used on the host.

Suggested-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20250220080215.49165-3-philmd@linaro.org>
[AJB: dropped whitespace cmd.py damage]
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20250304222439.2035603-10-alex.bennee@linaro.org>