Remove unused dependencies in build scripts

[alandefreitas]

The tests on s390x (#2389) failed because boost.coroutine doesn't work on s390x. To fix it (#2469) we need to conditionally remove the example targets that depend on coroutine.

Both the CMake and B2 scripts are globally linking all targets (even interface targets) to all dependency targets instead of linking only to the targets they depend on.

For instance, CMakeLists.txt links everything to Boost::coroutine and Jamfile links all tests and many examples to boost.coroutine, even though only a few examples depend on it.