objlib: Link object-files from `OBJECT` libraries.

Note: This finally links the object-files of the `OBJECT` library from
the right-hand side of `target_link_libraries` to the target on the
left-hand side. However, this will only happen with directly linked
`OBJECT` libraries, not with `OBJECT` libraries "linked" through
property `INTERFACE_LINK_LIBRARIES` of a target on the right-hand side!

Fixes: #14778