[CMake] MacOS and shared libraries from imported targets

[Michael Welsh Duggan]

I have a project that links against an external dynamic library for
which I have written a Find module that creates an import target.  I do
this, in part, by setting the IMPORTED_LOCATION property of the target
to the location of the dynamic library.

Unfortunately, on OSX the library shows up in the executable load
commands as an LC_LOAD_DYLIB of the raw filename (no directory) of the
shared library.  I expected it to use the whole path.  I tried setting
the INSTALL_NAME_DIR property to the directory containing the shared
library, but this changed nothing.

I will note that this is all still in the build location, as opposed to
post-install.  I am using the following settings currently:

set(CMAKE_SKIP_BUILD_RPATH false)
set(CMAKE_BUILD_WITH_INSTALL_RPATH false)
set(CMAKE_INSTALL_RPATH_USE_LINK_PATH true)
set(CMAKE_MACOSX_RPATH true)

I'm not 100% confident with how these options interact, so I am more
than prepared for someone to tell me that I am doing something wrong.
Any hints would be appreciated.

-- 
Michael Welsh Duggan
(mwd at cert.org)