[CMake] Target visibility in CMake using Xcode generator

[Holtgrewe, Manuel]

> While this works with Makefiles, I could imagine that the Xcode
> generator doesn't allow to build a (sub)project from within its
> directory if there're references to the parent project, especially
> targets. Since I don't have access to an Xcode installation at the
> moment, I cannot investigate this issue in further detail. BTW, is
> there a problem/badness/disadvantage to build target_b within the
> parent project, i.e. from A.xcodeproj?

Hm, my real-world story is a bit more complex. I think I understand better now what is going on and I might need to restructure my project a bit.

Thanks,
Manuel