If CMAKE_BUILD_TYPE is set, and user code contains:

 target_link_libraries(myexe prefix_$<$<CONFIG:Debug>:debug>)

then the computation with an empty config was computing a target-level
dependency on a target or library called prefix_, and a dependency
on a target or library called prefix_debug (as expected).

The existing logic skips 'prefix_' because it is not a known target,
and defers to the link-dependencies logic to find the library. The
link-dependencies logic does not incorrectly handle the config as
cmComputeTargetDepends did, and so did not encounter 'prefix_'
during its computation. This likely had no effect on the generated
buildsystem.