Fix parsing of sysroot id

Recent parsing changes introduced this regression.

Apertis: https://phabricator.apertis.org/T3777



Signed-off-by: Frédéric Dalleau <frederic.dalleau@collabora.com>
Reviewed-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D6383