Test non-IMPORTED libraries in the INTERFACE of IMPORTED libraries.

If a non-IMPORTED library is added to the INTERFACE_LINK_LIBRARIES
of a IMPORTED target, the non-IMPORTED target needs to become a
target dependency and link dependency of the consuming target.

This is already the case since commit 30962029 (Make targets depend
on the link interface of their dependees, 2012-12-26), so test that
it works.
Merge topic 'IMPORTED-build-dependencies' into next

35a450e Test non-IMPORTED libraries in the INTERFACE of IMPORTED libraries.