Add utility function to unwrap target if device

If the target is a device, we want to know whether to use a
sysroot or the SDK for configuration/debugging/etc.

Signed-off-by: Louis-Francis Ratté-Boulianne <lfrb@collabora.com>
Reviewed-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D5298