For the OLD CMP0022 behavior, we need to treat the implementation
as the interface when computing the interface libraries.  Make it
possible to do that without computing the link languages by adding
a new GetLinkImplementationLibraries method.  Extend the existing
GetLinkImplementation method to populate the languages if the
libraries have already been computed and cached.

Change GetTransitivePropertyTargets to invoke GetLinkInterfaceLibraries
instead of GetLinkInterface.  This is key, as it is a method called
by cmGeneratorExpressionEvaluator.

Change the cmGeneratorExpressionEvaluator to invoke
GetLinkImplementationLibraries instead of GetLinkImplementation.