Fix export of STATIC library PRIVATE non-target dependencies

In commit v3.5.0-rc1~43^2 (Fix export of STATIC library PRIVATE
dependencies with CMP0022 NEW, 2016-01-15) we taught
target_link_libraries to generate `$<LINK_ONLY:$<TARGET_NAME:dep>>` in
INTERFACE_LINK_LIBRARIES instead of `$<LINK_ONLY:dep>` so that `dep` can
be recognized as a target name and updated during export.  However, this
approach does not work when `dep` is just a plain library name and not a
target because `$<TARGET_NAME:...>` requires the name of a reachable
target.

Since we do not know during target_link_libraries whether the name will
correspond to a reachable target or not, we cannot inject the
`$<TARGET_NAME:...>` expression.  Revert this change and solve the
original problem instead by teaching the export logic to recognize and
update target names directly in `$<LINK_ONLY:...>` expressions.

Reported-by: Ben Boeckel <ben.boeckel@kitware.com>