CMake Nightly Date Stamp
Revert "Allow target_link_libraries with IMPORTED targets."

This reverts commit 9cfe4f1b769597bd9ba179eba46572a9df27f64c.

It turns out that correctly adding the content to
the IMPORTED_LINK_INTERFACE_LIBARIES_<CONFIG> of an upstream target
from the buildsystem of a downstream project is not simple.

If upstream had added the INTERFACE content, the config-specific
properties would  be determined by the DEBUG_CONFIGURATIONS of
upstream.

As downstream, we don't have any information about what
the DEBUG_CONFIGURATIONS of upstream were, so we can't determine
which configuration-specific properties to populate. The best we can do
is add it to all of them or add it to the ones downstream considers to
be DEBUG_CONFIGURATIONS, neither of which is a good solution.

So, removing the porcelain API for that is the best approach. A human
can still determine which properties to populate and use
the set_property API to populate the desired properies.

Another solution to this would be for upstream targets to publish
what they consider DEBUG_CONFIGURATIONS, but that can be added in
a future release.
Disallow porcelain to populate includes and defines of IMPORTED targets.

With similar reasoning to the parent commit, as downstreams, we can't
determine what $<CONFIG> generator expressions would be appropriate.

Upstream would have populated the INTERFACE_INCLUDE_DIRECTORIES with
config-specific generator expressions, possibly appropriate for
their DEBUG_CONFIGURATIONS. In theory, if we would add include
directories for a DEBUG intent, we would have to match the upstream
configurations for that.

Rather than attempting to discover the appropriate configurations
at this time, simplify the feature instead. The use of IMPORTED targets
with these commands could still be added in the future if targets
would export their DEBUG_CONFIGURATIONS somehow.
Merge topic 'disallow-IMPORTED-interface-porcelain' into next

b98d14d Disallow porcelain to populate includes and defines of IMPORTED targets.
48a4cf2 Revert "Allow target_link_libraries with IMPORTED targets."
3ded614 CMake Nightly Date Stamp