On some systems IMPORTED_LOCATION isn't set, but configuration-specific
locations like IMPORTED_LOCATION_RELEASE are. In these cases, fall back to
the location of the release build if the default isn't found.
Fixes the build on Arch Linux.
Change-Id: Iff87a8356302a260b2ac5f959f835d1cdf8a5c65
Reviewed-by: Eike Ziller <eike.ziller@qt.io>