[CMake] Linking a library that is made by cmake

[Petr Bena]

I have a project:

/Target A
- CMakeLists.txt
- /Target B
-- CMakeLists.txt
- /Target C
-- CMakeLists.txt

So, A is including B and C using add_subdirectory. However, A is
producing 2 targets, one of which is a library and I need to link B
and C against that library. How would I do that?