[CMake] Visual Studio and dependy on imported library

[Tim Kettler]

Hi,

imagine a project that declares an imported library (#implib#) in a 
subdirectory. The imported library
depends on some other target (#lib#). A second imported library 
(#implibtop#) with the same dependency is
declared in the top-level CMakeLists.txt. Additionally there are three 
executables that each depend on one
of the library targets. An example project is available at Github [1].

With CMake 3.7.2 and Visual Studio 2015 I'm seeing the following project 
dependencies in the solution:

- execlib (target_links #lib#) depends on the #lib# target
- execimplib (target_links #implib#) does not depend on the #lib# target
- execimplibtop (target_links #implibtop#) depends on the #lib# target

Is this the expected behaviour? Why is #execimplib# not picking up the 
dependency?

I discoverd this while creating a wrapper imported library for an 
external project.

-Tim

[1] https://github.com/tik/cmake-implib