We represent stub libraries, e.g., for CUDA, using imported `SHARED`
library targets with only `IMPORTED_IMPLIB`, and no `IMPORTED_LOCATION`,
to indicate that the stub file is meant only for linkers and not dynamic
loaders.  See commit 7351d590 (cmTarget: Add a way to represent
imported shared library stubs, 2023-07-17, v3.28.0-rc1~344^2) and commit
fc650892 (cmComputeLinkInformation: Restore soname lookup for
non-imported targets, 2023-12-05, v3.28.0~4^2).

If a shared library is linked to a stub, it has a `NEEDED` field
populated with the `SONAME` found in the stub.  When a dependent target
links to such a shared library, some linkers want to find a library file
on disk and load it to see what symbols it provides.  This is necessary
for linkers that enforce `--no-allow-shlib-undefined`.  On hosts with
only the stub library installed, e.g., with only the CUDA toolkit
development package, the real runtime library corresponding to the
stub's `SONAME` may not even exist, so no `-rpath-link` flag can help
linkers find it.  Pass the stub library to linkers explicitly so they
can find it without searching.